IN  MEMORIAM 
FLOR1AN  CAJORI 


1 


T 

THE 

RECENT    PROGRESS 


OP 


ASTRONOMY; 


ESPECIALLY 


IN  THE   UNITED   STATES. 


BY  ELIAS  LOOMIS,  LLD., 


PBOFE380E  OF  MATHEMATICS    AJfD    XATUEAL    PHILO8OPHT    IK    TUB    TTN1VEB8ITY    OF 
CITT  OF  NEW  TOBK,   AXD  ATJTHOB  OF   A  COTTESS   OF  MATHEMATICS. 


THIRD    EDITION, 

MOSTLY    RE-WBITTEM,     AND    MUCH    E  N  I.  A  B  G  E  D  . 


NEW  YOKK: 
HARPER  &  BROTHERS, 

329  TO  335  PEAEL  STREET. 
1856. 


Entered,  according  to  Act  of  Congress,  in  the  year  1856,  by 

HARPER    AND    BROTHERS, 
In  the  Clerk's  Office  for  the  Southern  District  of  New  York. 


PREFACE. 

THE  progress  of  astronomical  discovery  was  never  more  rapid 
than  during  the  last  fifteen  years.  Within  this  period,  the 
number  of  known  members  of  the  planetary  system  has  been 
more  than  doubled.  A  planet  of  vast  dimensions  has  been 
added  to  our  system  ;  thirty-six  new  asteroids  have  been  dis- 
covered; four  new  satellites  have  been  detected;  and  a  new 
ring  has  been  added  to  Saturn. 

It  is  especially  gratifying  to  note  the  progress  which  the 
last  few  years  have  witnessed  in  the  United  States,  both  in  the 
facilities  for  observation,  and  in  the  number  of  active  observers. 
It  is  but  twenty-five  years  since  t  the  first  telescope,  exceeding 
those  of  a  portable  size,  was  imported  into  the  United  States  ; 
and  the  introduction  of  meridional  instruments  of  the  larger 
class  is  of  still  more  recent  date.  Now  we  have  one  telescope 
which  acknowledges  no  superior  ;  and  we  have  several  which 
would  be  esteemed  worthy  of  a  place  in  the  finest  observatories 
of  Europe.  We  have  also  numerous  meridional  instruments,  of 
dimensions  adequate  to  be  employed  in  original  research.  Our 
own  artists  have  entered  successfully  upon  the  manufacture  of 
refracting  telescopes  of  the  largest  size,  and  have  received  the 
highest  commendation  from  some  of  the  best  judges  in  Europe. 
These  instruments  have  not  remained  wholly  unemployed.  At 
the  observatories  of  Washington  and  Cambridge,  extensive  cata- 


9 


iy  PEE  FACE. 

logues  of  stars  are  now  in  progress ;  while  nearly  every  known 
member  of  our  solar  system  has  been  repeatedly  and  carefully 
observed.  These  observations  are  all  permanently  recorded  by 
a  simple  touch  of  the  finger  upon  a  key  which  closes  an 
electric  circuit — a  method  recently  introduced  at  Greenwich 
observatory,  and  known  everywhere  throughout  Europe  by  the 
distinctive  name  of  the  American  method. 

Numerous  discoveries  have  been  the  result  of  this  astronomical 
activity.  A  large  number  of  comets  have  been  independently 
discovered  on  this  side  of  the  Atlantic  ;  and  among  these,  three 
at  least  were  observed  here  before  they  were  seen  in  Europe. 
The  two  nebulae  which  have  been  longest  and  best  known,  were 
never  adequately  figured  until  they  were  observed  by  the  Messrs. 
Bond ;  and  the  planet  Saturn,  which  for  many  years  was  made 
the  subject  of  special  study  by  the  elder  Herschel,  with  his 
wonderful  means  of  observation,  first  revealed  to  the  Messrs. 
Bond  a  new  ring  and  an  eighth  satellite.  The  novel  spectacle 
of  a  comet  divided  into  two  nearly  equal  portions,  was  first 
witnessed  in  America ;  and  an  American  observer  has  added 
one  to  the  long  list  of  planetary  discoveries. 

Let  us  indulge  the  hope  that  the  future  progress  of  as- 
tronomy is  to  be  no  less  brilliant  than  the  past ;  and  that 
henceforth  America  may  be  even  more  distinguished  for  her 
contributions  to  science,  than  for  her  progress  in  material 
power  and  wealth. 


CONTENTS. 


CHAPTER    L 

RECENT  ADDITIONS  TO  OUR  KNOWLEDGE  OF  THE 
PLANETARY  SYSTEM. 

SECTION  I. 

PAOB 

THE  DISCOVERT  OP  THE  PLANET  NEPTUNE, 9 

Irregularities  in  the  motion  of  Uranus,   . 10 

Labors  of  Mr.  Adams, 15 

Researches  of  M.  Le  Verrier, 16 

Discovery  of  the  Planet  by  Dr.  Galle 22 

Search  for  old  observations, 25 

True  orbit  of  the  Planet, 30 

Name  given  to  the  Planet, 31 

Is  Neptune  surrounded  by  a  ring  ? 36 

Discovery  of  a  Satellite, 38 

Will  Neptune  account  for  the  anomalies  of  Uranus  ?         ...  40 

Is  Neptune  the  Planet  predicted  by  Le  Terrier  ?    .  42 

Why  was  not  the  Planet  sooner  discovered  ? 50 


SECTION  H. 

ZONE  OF  PLANETS  BETWEEN  MAES  AND  JUPITER,    ....  54 

Discovery  of  thirty-sir  new  Asteroids, 63 

Elements  of  the  Asteroids, 83 

Are  they  all  fragments  of  a  single  body  ? 86 

Relation  of  the  Asteroids  to  each  other, 90 


SECTION  in. 
DISCOVERY  OF  AN  EIGHTH  SATELLITE  OF  SATURN,  ....      96 

SECTION  IV. 
OF  THE  SATELLITES  OF  URANUS,  ....  .  100 

SECTION  Y. 
DISCOVERY  OF  A  NEW  RING  TO  SATURN, 108 


.VI  CONTENTS. 

CHAPTER    II. 

RECENT  ADDITIONS  TO  OUR  KNOWLEDGE  OF  COMETS. 
SECTION  I. 

PAQB 

THE  GREAT  COMET  OP  1843, 121 

Seen  at  noon-day, 121 

Orbit  of  this  Comet, 125 

Has  this  Comet  been  seen  before  ? .129 

SECTION  H. 
FATE'S  COMET  OF  1843,        .       .     - 132 

SECTION  III. 
DE  Yico's  COMET  OP  1841,     .     •  . 136 

SECTION  IY. 

BIELA'S  COMET 140 

Double  appearance  of  this  Comet  in  1846, 141 

Relation  of  these  two  bodies,          .        .        .        .        .        .        .  143 

Appearance  of  the  Comet  in  1852,     .......  144 

Cause  of  the  separation, 146 

SECTION  V. 
Miss  MITCHELL'S  COMET, 150 

SECTION  VI. 
EXPECTED  RETURN  OP  THE  COMET  OP  1264,         .       .       .       .        153 

SECTION  VII. 
THE  GREAT  COMET  OP  1853, 15T 

CHAPTER    III. 

ADDITIONS  TO   OUR   KNOWLEDGE   OF  FIXED   STARS  AND 
NEBULA. 

SECTION   I. 

DETERMINATION  OP  PARALLAX  OP  FIXED  STARS,  ....        159 
Bessel's  determination  of  the  parallax  of  61  Cygni,    .        .        .        .161 


CONTENTS.  Vll 

PAGB 

Parallax  of  a  Centauri, 163 

Parallax  of  a  Lyrae  and  other  stars, .  .        .164 

SECTION  II. 

OBSERVATIONS  OP  NEW  AND  VARIABLE  STABS,    .       .        .       .        170 

The  star  Eta  Argils, 170 

Hind's  star  of  1848, 172 

Kepler's  star  of  1604, ,        .        .173 

SECTION  HI. 

DISTRIBUTION  OP  THE  STARS  IN  SPACE, 175 

Herschel's  view  of  the  Milky  Way, ,     .        .175 

Abandoned  by  its  author  in  1817, ,        .         179 

Struve's  researches  on  the  Milky  Way, 180 

Sir  J.  Herschel's  observations  in  the  Southern  hemisphere,     .        .        182 

SECTION  IV. 

MOTION  OP  THE  SUN  AND  FIXED  STARS, 189 

Point  of  space  toward  which  the  Sun  is  moving,     .        .        .        ,        190 
Madler's  speculations  respecting  the  Central  Sun,      .  191 


SECTION  V. 

RESOLUTION  OF  REMARKABLE  NEBULJS, 196 

Lord  Rosse's  telescope, 197 

Various  nebulae  resolved, 198 

Nebulae  resolved  by  the  Cambridge  telescope, 200 


CHAPTER    IV. 

PROGRESS   OF  ASTRONOMY  IN  THE  UNITED  STATES. 
SECTION  I. 

HISTORY  OP  AMERICAN  OBSERVATORIES, 202 

Transit  of  Venus  in  1769, 202 

Yale  College  observatory, 206 

Williams  College  observatory, 208 

Western  Reserve  College  observatory, 210 

Philadelphia  High  School  observatory, 213 

West  Point  observatory, 219 

National  observatory  at  Washington, 223 

Georgetown  observatory,  D.  C.,  .        .        .•       .        .        .  237 

Cincinnati  observatory, 241 

Cambridge  observatory, 244 

Sharon  observatory,  near  Philadelphia, 256 


Viii  CONTENTS. 


Tuscaloosa  (Alabama)  observatory, 258 

Mr.  Rutherford's  observatory,  New  York, 260 

Friends'  observatory,  Philadelphia, 262 

Amherst  College  observatory, 263 

Charleston  (South  Carolina)  observatory, 264 

Dartmouth  College  observatory, 265 

Mr.  Yan  Arsdale's  observatory, 270 

Shelby  College  observatory, 212 

Buffalo  observatory, 273 

Mr.  Campbell's  observatory,  New  York, 275 

Observatory  of  Michigan  University, 277 

Cambridge  (Cloverden)  observatory, 2  SO 

Dudley  observatory  at  Albany, 281 

Hamilton  College  observatory,  .        . 284 

SECTION  IL 

ASTRONOMICAL  EXPEDITION  TO  CHILI,  .        .       .       .    •  .       .  293 

SECTION  III. 
ASTRONOMICAL  RESULTS  or  PUBLIC  SURVEYS,         .        .       .       .300 

SECTION  IT. 

APPLICATION  OF  THE  ELECTRIC  TELEGRAPH  TO  ASTRONOMICAL  USES,  304 

Experiments  between  New  York  and  "Washington,         .        .        .  305 
Experiments  between  New  York  and  Cambridge,     .        .         .        .310 

The  electric  circuit  broken  by  a  clock, 313 

Mode  of  registering  the  observations, 325 

Observations  for  longitude  since  the  autumn  of  1848,     .        .        .  330 

Application  of  the  electric  circuit  to  astronomical  observations,          .  341 

Application  of  the  electric  circuit  to  astronomical  uses  in  Europe,  .  345 
Experiments  made  in  Europe  for  the  determination  of  geographical 

longitude  by  the  electric  telegraph, 349 

Determination  of  the  velocity  of  the  electric  current,      .        .        .  357 
Differences  of  declination  recorded  by  electro-magnetism,  .        .        .364 

SECTION  V. 

ASTRONOMICAL  PUBLICATIONS, 368 


SECTION  YL 

THE  MANUFACTURE  OF  TELESCOPES  IN  THE  UNITED  STATES,  .        .375 

Reflecting  telescopes, 375 

Refracting  telescopes,        .        .         . 377 

Manufacture  of  glass  for'optical  purposes, 378 

Fitz's  telescopes, 385 

Clarke's  telescopes,         .        . 389 

Spencer's  telescopes, .  392 


CHAPTER   I. 


RECENT    ADDITIONS    TO    OUR    KNOWLEDGE    OF    THE 
PLANETARY    SYSTEM. 


SECTION   I. 

THE   DISCOVERY   OF   THE   PLANET   NEPTUNE. 

THE  discovery  of  the  planet  Neptune  took  place  un- 
der circumstances  most  extraordinary.  The  existence 
of  the  planet  was  predicted,  its  path  in  the  heavens  was 
assigned,  its  mass  was  calculated,  from  considerations 
purely  theoretical.  The  astronomer  was  told  where  to 
direct  his  telescope,  and  he  would  see  a  planet  hitherto 
unobserved.  The  telescope  was  pointed,  and  there  the 
planet  was  found.  In  the  whole  history  of  astronomy 
we  can  find  few  things  equally  wonderful.  This  dis- 
covery resulted  from  the  study  of  the  motions  of  the 
planet  Uranus. 

Uranus  was  first  discovered  to  be  a  planet  in  1781, 
but  it  had  been  repeatedly  observed  before  by  different 
astronomers,  and  mistaken  for  a  fixed  star.  Nineteen 
observations  of  this  description  are  on  record,  one  of 
them  dating  as  far  back  as  1690,  In  1821,  M.  Bouvard, 
:>f  Paris,  published  a  set  of  tables  for  computing  the 

1* 


10  HISTORY  OF  ASTRONOMY. 

place  of  this  planet.  The  materials  for  the  construction 
of  these  tables  consisted  of  forty  years'  regular  obser- 
vations at  Greenwich  and  Paris  since  1781,  and  the 
nineteen  accidental  observations,  reaching  back  almost 
a  century  further.  Upon  comparing  these  observations, 
Bouvard  found  unexpected  difficulties.  He  was  unable 
to  find  any  elliptic  orbit,  which,  combined  with  the 
perturbations  by  Jupiter  and  Saturn,  would  represent 
both  the  ancient  and  the  modern  observations.  When 
he  attempted  to  unite  the  ancient  with  the  modern 
observations,  the  former  might  be  tolerably  well  re- 
presented, but  the  latter  exhibited  discordances  too  great 
to  be  ascribed  to  errors  of  observation.  Not  being 
able  to  explain  this  discrepancy  in  any  satisfactory  man- 
ner, he  rejected  the  ancient  observations,  and  founded 
his  tables  upon  the  observations  since  1781.  "  It  being 
necessary,"  says  he,  "to  decide  between  the  ancient  and 
the  modern  observations,  I  have  held  to  the  modern 
ones  as  being  the  most  likely  to  be  accurate,  and  I  leave 
it  to  time  to  show  whether  the  difficulty  of  reconciling 
the  two  sets  of  observations  depends  .  upon  the  inac- 
curacy of  the  ancient  ones,  or  on  some  foreign  and  un- 
known influence  to  which  the  pla.net  is  subjected" 

These  tables  represent  very  well  the  observations  of 
the  forty  years  from  which  they  were  derived ;  but 
soon  after  1821,  new  discrepancies  began  to  appear, 
which  have  lately  increased  with  great  rapidity.  In 
1832,  the  discordance  between  the  observed  and  com- 
puted plaoe  of  tlje  planet,  Amounted  to  nearly  half  a 


THE  PLANET  NEPTUNE.  11 

minute  of  space,  and  now  the  error  exceeds  two  min- 
utes. In  order  to  exhibit  more  palpably  the  nature 
of  these  discrepancies,  I  have  represented  them  upon 
the  jfigure  on  the  next  page.  If  the  straight  line, 
A  B,  be  taken  to  represent  the  path  of  Uranus,  as 
computed  from  the  elements  of  Bouvard,  the  broken 
line  will  represent  the  observed  orbit.  The  deviation 
of  these  two  lines  indicates  the  discrepancy  between 
theory  and  observation  for  the  dates  at  the  top  of  the 
page,  the  amount  of  the  discrepancy  being  given  on  the 
left  margin.  If  it  was  doubtful  whether  this  difference 
in  the  case  of  the  ancient  observations  was  not  due  to 
the  carelessness  of  the  observers,  no  such  supposition 
is  admissible  in  the  case  of  the  observations  since 
1821.  The  discrepancy  between  Bouvard's  orbit  and 
the  observations  is  now  enormous,  and  is  increasing 
with  alarming  rapidity. 

What  can  be  the  cause  of  these  discrepancies?  Do 
they  indicate  errors  in  the  computations  of  M.  Bouvard  ? 
In  order  to  decide  this  question,  the  illustrious  Bessel, 
about  the  year  1840,  subjected  all  the  observations  to 
a  new  calculation ;  and  although  he  detected  one  or 
two  errors  of  Bouvard,  they  did  not  materially  influ- 
ence the  results.  He  satisfied  himself  that  the  ancient 
and  modern  observations  could  not  be  reconciled  by 
any  modification  of  the  elements,  and  that  the  differ- 
ences could  not  be  attributed  to  inaccuracy  of  instru- 
ments, or  to  methods  of  observation.  Are  these  anom- 
alies due  to  the  attraction  of  some  unknown  disturb- 


12 


HISTOKY  OF  ASTKONOMY. 


So 


2     g    § 

GO         QO        00 


7 


-2(7" 
-30" 


\ 


\7 


•80" 
10* 

-ttf 

-130" 


Iff 


THE  PLANET  NEPTUNE.  13 

ing  body  ?  This  idea  was  seriously  entertained  more 
than  twelve  years  ago  by  Bouvard,  Hansen,  Hussey, 
Bessel,  and  some  others.  In  a  public  lecture  delivered 
in  the  year  1840,  Bessel  stated,  "  I  have  arrived  at  the 
full  conviction  that  we  have  in  Uranus  a  case  to  which 
Laplace's  assertion,  that  the  law  of  gravitation  entirely 
explains  all  the  motions  observed  in  our  solar  system,  is 
inapplicable.  We  have  here  to  do  with  discordances 
whose  explanation  can  only  be  found  in  a  new  physical 
discovery.  Further  attempts  to  explain  them  must  be 
based  upon  the  endeavor  to  discover  an  orbit  and  a 
mass  for  some  unknown  planet,  of  such  a  nature,  that 
the  resulting  perturbations  of  Uranus  may  reconcile  the 
present  want  of  harmony  in  the  observations." 

Dr.  T.  J.  Hussey,  in  1834,  proposed  to  compute  an. 
approximate  place  of  the  supposed  disturbing  body,  and 
then  commence  searching  for  it  with  his  large  reflector. 
Mr.  Airy,  now  Astronomer  Royal  of  Great  Britain,  at 
that  time  professor  in  Cambridge,  pronounced  the  prob- 
lem hopeless.  His  words  were  :  "If  it  were  certain  that 
there  was  any  extraneous  action  upon  Uranus,  I  doubt 
much  the  possibility  of  determining  the  place  of  the 
planet  which  produced  it.  /  am  sure  it  could  not  be  done 
till  the  nature  of  the  irregularity  was  well  determined  from 
several  successive  revolutions  /"  that  is,  till  after  the  lapse 
of  several  centuries. 

This  deliberate  opinion  from  one  who,  by  common 
consent,  stood  at  the  head  of  British  mathematicians  and 
astronomers,  would  have  deterred  any  but  the  most 


14  HISTORY  OF  ASTRONOMY. 

daring  mathematician  from  attacking  the  problem. 
Again,  in  1837,  Mr.  Airy  repeats  the  same  idea:  "If 
these  errors  are  the  effect  of  any  unseen  body,  it  will 
be  nearly  impossible  ever  to  find  out  its  place.11 

In  the  year  1842,  the  Eoyal  Society  of  Sciences  of 
Gottingen,  proposed,  as  a  prize  question,  the  full  discus- 
sion of  the  theory  of  the  motions  of  Uranus,  with 
special  reference  to  the  cause  of  the  large  and  increas- 
ing error  of  Bouvard's  tables.  During  the  same  year, 
1842,  Bessel  was  engaged  in  researches  relative  to  this 
problem ;  but  his  labors  were  soon  interrupted  by  sick- 
ness and  subsequent  death ;  and  from  this  time  we  find 
but  two  mathematicians,  Mr.  Adams,  of  Cambridge 
University,  in  England,  and  M.  Le  Yerrier,  of  Paris,  who 
.busied  themselves  with  the  problem. 

It  should  be  remembered,  that  in  accordance  with  the 
Newtonian  law  of  gravitation,  every  body  in  the  solar 
system  attracts  every  other ;  that  the  attraction  of  each 
body  is  proportioned  to  its  quantity  of  matter ;  and  that 
in  the  same  body  the  power  of  attraction  varies  in- 
versely as  the  square  of  the  distance.  In  order,  there- 
fore, to  compute  the  exact  place  of  a  planet  in  its  orbit 
about  the  sun,  it  is  necessary  not  merely  to  regard  the 
attraction  of  the  central  body,  but  also  to  allow  for  the 
influence  of  all  the  other  bodies  of  the 
solar  system.  For  instance,  if  the  sun 
alone  had  acted,  Jupiter  would  revolve 
around  the  central  luminary  in  a  perfect 
ellipse,  which  we  may  represent  by  the 
annexed  black  curve;  but  the  real  orbit 


THE  PLANET  NEPTUNE.  15 

vibrates  around  this  curve  as  in  the  dotted  line,  a  curve 
which  is  not  reproduced  at  every  revolution,  but  will 
pass  through  an  indefinite  number  of  variations.  To 
compute  the  exact  orbit  which  a  planet  will  describe, 
subject  to  the  attractions  of  all  the  members  of  the  solar 
system,  is  one  of  the  grandest  problems  in  astronomy. 

Hitherto  mathematicians  had  only  aspired  to  compute 
the  disturbing  influence  of  one  body  upon  another,  when 
the  magnitude  and  position  of  both  bodies  were  known. 
But,  in  the  case  of  Uranus,  it  was  necessary  to  solve  the 
inverse  problem  which  Professor  Airy  had  pronounced 
hopeless,  viz.,  from  the  observed  disturbances  of  one 
body,  to  compute  the  place  of  the  disturbing  body. 

After  taking  his  degree  of  Bachelor  of  Arts  in  Jan- 
uary, 1843,  with  the  honor  of  Senior  "Wrangler,  Mr. 
Adams  ventured  to  attack  this  problem,  and  obtained 
an  approximate  solution  by  supposing  the  disturbing 
body  to  move  in  a  circle  at  twice  the  distance  of 
Uranus  from  the  sun.  His  results  were  so  far  satis- 
factory, as  to  encourage  him  to  attempt  a  more  complete 
solution.  Accordingly,  in  February,  1844,  having  ob- 
tained through  Professor  Airy  a*  complete  copy  of  the 
Greenwich  observations  of  Uranus,  from  1754  to  1830, 
he  renewed  his  computations,  which  he  continued  dur- 
ing that  and  the  subsequent  years.  In  September,  1845, 
he  had  obtained  the  approximate  orbit  of  the  disturbing 
planet,  which  he  showed  to  Professor  Challis,  the  director 
of  the  observatory  at  Cambridge ;  and  near  the  close  of 
the  next  month,  he  communicated  his  results  to  the 


16  HISTORY  OF  ASTRONOMY. 

Astronomer  Koyal,  together  with  a  comparison  of  his 
theory  with  the  observations.  The  discrepancies  were 
quite  small,  except  for  the  single  observation  of  1690, 
which  differed  by  44";  this  observation  not  having  been 
used  in  the  equations  of  condition.  Professor  Airy, 
in  acknowledging  the  receipt  of  this  letter,  pronounced 
the  results  extremely  satisfactory,  and  inquired  of  Mr. 
Adams  whether  his  theory  would  explain  the  error  of 
the  tables  in  regard  to  the  distance  of  Uranus  from  the 
sun,  which  error  he  had  shown  to  be  very  great.  To 
this  inquiry  Mr.  Adams  returned  no  answer  for  nearly 
a  year ;  probably  because  he  was  not  able  to  answer  the 
question  entirely  to  his  own  satisfaction. 

Meanwhile,  this  grand  problem  was  undertaken  by 
another  mathematician  who  was  entirely  ignorant  of  the 
progress  which  Mr.  Adams  had  made ;  for  none  of  his 
results  had  yet  been  published.  In  the  summer  of  1845, 
M.  Arago,  of  Paris,  requested  M.  Le  Yerrier,  a  young 
mathematician,  who  had  already  distinguished  himself 
by  his  improved  tables  of  Mercury,  to  attempt  the  solu- 
tion of  this  problem.  This  he  accordingly  did,  and  his 
success  astonished  all -Europe.  He  commenced  his  in- 
vestigations by  inquiring  whether  the  observations  of  • 
Uranus  could  be  reconciled  with  the  supposition,  that 
this  body  is  subject  to  no  other  attraction  than  that  of 
the  sun  and  the  known  planets,  acting  according  to  the 
Newtonian  law  of  gravitation.  He  carefully  computed 
the  effects  due  to  the  action  of  Jupiter  and  Saturn, 
neglecting  no  quantities  until  he  had  proved  that  their 


THE  PLANET  NEPTUNE.  17 

influence  was  insensible.  He  thus  discovered  some  im- 
portant terms  which  had  been  neglected  by  Laplace. 
He  then  compared  his  theory  with  observation,  and 
proved  conclusively  that  the  observations  of  Uranus 
could  not  be  reconciled  with  the  law  •  of  gravitation, 
except  by  admitting  some  extraneous  action.  These  re- 
sults were  communicated  to  the  Academy  of  Sciences, 
Nov.  10,  1845 ;  and  such  was  the  reputation  secured 
by  this  and  his  preceding  memoirs,  that  in  January, 
1846,  he  was  elected  to  fill  the  vacancy  which  had  oc- 
curred in  the  Institute  in  the  section  of  Astronomy,  by 
the  death  of  Cassini.  This  memoir  was  but  preliminary 
to  his  grand  investigation  ;  and  it  should  be  remarked, 
that  Mr.  Adams  had  already  deposited  with  the  Astron- 
omer Koyal  at  Greenwich,  a  paper  containing  the  ele- 
ments of  the  supposed  disturbing  planet,  and  agreeing 
closely  with  the  results  which  Le  Yerrier  subsequently 
obtained. 

]^e  Yerrier  next  proceeds  to  inquire  after  the  cause 
of  the  discovered  irregularities.  Is  it  possible  that  at 
the  immense  distance  of  Uranus  from  the  sun,  the  force 
of  attraction  does  not  vary  inversely  as  the  square  of 
the  distance?  The  law  of  gravitation  is  too  firmly 
established  to  permit  such  a  supposition,  until  every 
other  resource  has  failed.  Are  these  irregularities  due 
to  the  resistance  of  a  rare  ether  diffused  everywhere 
through  space?  No  other  planet  has  afforded  any  in- 
dication of  such  a  resistance.  Can  they  be  ascribed  to 
a  great  satellite  accompanying  the  planet  ?  Such  a  cause 


18  HISTORY   OF  ASTRONOMY. 

would  produce  inequalities  having  a  very  short  period ; 
while  the  observed  anomalies  of  Uranus  are  precisely 
the  reverse.  Moreover,  it  would  be  necessary  to  assign 
it  such  dimensions  that  it  could  not  fail  to  have  been 
visible  in  our  telescopes.  Has  a  comet  impinged  upon 
Uranus,  and  changed  the  form  of  its  orbit?  Such  a 
cause  might  render  it  impossible  to  represent  the  en- 
tire series  of  observations  by  a  single  elliptic  orbit; 
but  the  observations  before  the  supposed  collision,  would 
all  be  consistent  with  each  other,  and  the  observations 
after  collision  would  also  be  consistent  with  each  other. 
Yet  the  observations  of  Uranus  from  1781  to  1821,  as 
may  be  seen  from  the  diagram,  page  12,  accord  neither 
with  the  earlier  observations  nor  with  the  more  recent 
ones. 

There  seems  to  remain  no  other  probable  supposition 
than  that  of  an  undiscovered  planet.  But  if  these  disturb- 
ances are  due  to  such  a  body,  we  can  not  suppose  it 
situated  within  the  orbit  of  Saturn.  This  would  disturb 
the  orbit  of  Saturn  more  than  that  of  Uranus,  while  we 
know  that  its  influence  on  Saturn  is  inappreciable,  for 
Saturn's  motion  is  well  represented  by  the  tables.  Can 
this  body  be  situated  between  Saturn  and  Uranus?  We 
must  then  place  it  much  nearer  Uranus  than  Saturn,  for 
the  reason  already  assigned,  in  which  case  its  mass  must 
be  supposed  to  be  small,  or  it  would  produce  too  great 
an  effect  upon  Uranus.  Under  these  circumstances,  its 
action  would  only  be  appreciable  when  in  the  imme- 
diate neighborhood  of  Uranus,  which  supposition  does 


THE   PLANET   NEPTUNE.  19 

not  accord  well  with  the  observations.  The  disturbing 
body  must  then  be  situated  beyond  Uranus,  and  at  a 
considerable  distance  from  it,  for  reasons  already  given. 
Now  the  distance  of  each  of  the  more  remote  planets 
from  the  sun,  is  about  double  that  of  the  preceding  one. 
It  is  natural,  tken;  to  conjecture  that  the  disturbing 
planet  may  be  at  a  distance  from  the  sun  double  that 
of  Uranus,  and  it  must  move  nearly  in  the  ecliptic,  be- 
cause the  observed  inequalities  of  Uranus  are  chiefly  in 
the  direction  of  the  ecliptic.  Le  Yerrier  then  propounds 
the  following  specific  problem : 

"  Are  the  irregularities  in  the  motion  of  Uranus  due  to 
the  action  of  a  planet  situated  in  the  ecliptic,  at  a  distance 
from  the  sun  double  that  of  Uranus  f  If  so,  what  is  its 
present  place,  its  mass,  and  the  elements  of  its  orbit  ?"  This 
problem  he  proceeds  to  resolve. 

If  we  could  determine  for  each  day  the  precise  effect 
produced  by  the  unknown  body,  we  could  deduce  from 
it  the  direction  in  which  Uranus  is  drawn;  that  is,  we 
should  know  the  direction  of  the  disturbing  body.  But 
the  problem  is  far  from  being  thus  simple.  The  amount 
of  the  disturbance  can  not  be  deduced  directly  from  the 
observations,  unless  we  know  the  exact  orbit  which 
Uranus  would  describe,  provided  it  were  free  from  this 
disturbing  action;  and  this  orbit  in  turn  can  not  be 
computed  unless  we  know  the  amount  of  the  disturb- 
ance. Le  Yerrier  therefore  computes  for  every  nine 
degrees  of  the  entire  circumference,  the  effect  which 
would  be  produced  by  supposing  a  planet  situated  in 


20  HISTORY   OF  ASTEONOMY. 

different  parts  of  the  ecliptic.  He  finds  that  when  he 
locates  the  supposed  disturbing  planet  in  one  part  of  the 
ecliptic,  the  discrepancies  between  the  observed  and 
computed  effects  are  enormous.  By  varying  the  place 
of  the  planet,  the  discrepancies  become  smaller,  until  at 
a  certain  point  they  nearly  disappear.  Hence  he  con- 
cludes that  there  is  but  one  point  of  the  ecliptic  where 
the  planet  can  be  placed,  so  as  to  satisfy  the  observations 
of  Uranus.  Having  thus  determined  its  approximate 
place,  he  proceeds  to  compute  more  rigorously  its  effects ; 
and  on  the  first  of  June,  1846,  he  announces  as  the 
result  of  his  investigations,  that  the  longitude  of  the 
disturbing  planet  for  the  beginning  of  1847,  must  be 
about  325°. 

The  result  thus  obtained  by  Le  Terrier,  differed  but 
one  degree  from  that  communicated  by  Mr.  Adams 
to  Professor  Airy,  more  than  seven  months  previous. 
Upon  receiving  this  intelligence,  Professor  Airy  ex- 
pressed himself  satisfied  with  regard  to  the  general  ac- 
curacy of  both  computations,  and  immediately  wrote  to 
Le  Verrier,  inquiring,  as  he  had  done  before  of  Mr. 
Adams,  whether  his  theory  explained  the  error  of  the 
tables  in  respect  to  the  distance  of  Uranus  from  the  sun. 
Le  Verrier  answered  that  the  errors  of  radius- vector  must 
be  accounted  for,  inasmuch  as  the  equations  of  condition 
depended  on  observations  at  the  quadratures  as  well  as  at 
the  oppositions.  Professor  Airy  was  now  so  well  con- 
vinced of  the  existence  of  a  planet  yet  undiscovered,  that 
he  was  anxious  to  have  a  systematic  search  for  it  forth- 


THE  PLANET  NEPTUNE.  21 

with  undertaken.  The  observatory  of  Cambridge  is 
provided  with  one  of  the  finest  telescopes  of  Europe, 
presented  by  the  late  Duke  of  Northumberland.  Pro- 
fessor Airy  urged  upon  the  director,  Professor  Challis, 
to  undertake  the  desired  search;  and  recommended  the 
examination  of  a  belt  of  the  heavens  ten  degrees  in 
breadth,  and  extending  thirty  degrees  in  the  direction  of 
the  ecliptic.  This  belt  was  to  be  swept  over  at  least 
three  times.  If  any  star  in  the  second  sweep  had  a  dif- 
ferent position  from  that  observed  in  the  first,  it  might 
be  presumed  that  it  was  the  planet.  If  two  sweeps 
failed  of  detecting  the  planet,  it  might  be  caught  in  the 
third. 

Professor  Challis  commenced  his  search  July  29th,  and 
continued  it  each  favorable  evening,  recording  the  exact 
position  of  every  star  down  to  the  eleventh  magnitude. 
Meanwhile  Le  Yerrier  was  proceeding  with  his  computa- 
tions, and  on  the  31st  of  August  he  announced  to  the 
Academy  the  elements  he  had  obtained  for  the  sup- 
posed planet.  He  assigned  its  exact  place  in  the  heav- 
ens, and  estimated  that  it  should  appear  as  a  star  of 
the  eighth  magnitude,  with  an  apparent  diameter  of 
about  three  seconds ;  and,  consequently,  that  the  planet 
ought  to  be  visible  in  good  telescopes,  and  with  a  per- 
ceptible disc.  The  fixed  stars  are  situated  at  such  im- 
mense distances  from  us,  that  to  the  most  powerful 
telescopes  they  appear  only  as  points,  although  with  a 
brilliancy  augmented  in  proportion  to  the  size  of  the  tel- 
escope; while  all  the  planets  exhibit  a  measurable  disc. 


22  HISTORY  OF  ASTRONOMY. 

*   •     ,  v  '    *' , 

Le  Verrier  was  of  opinion  that  the  new  planet  might  be 
found  by  its  possession  of  a  visible  disc,  and  therefore 
without  any  very  great  labor. 

Soon  after  this  communication  was  made  to  the 
Academy,  Le  Verrier,  in  acknowledging  the  receipt  of 
a  memoir,  made  use  of  the  opportunity  thus  afforded  to 
request  Dr.  Galle,  of  the  Berlin  observatory  (where  is 
found  one  of  the  largest  telescopes  of  Europe),  to  under- 
take a  search  for  his  computed  planet,  and  he  assigned  its 
supposed  place  in  the  heavens.  The  Berlin  Academy 
had  just  published  a  chart  of  this  part  of  the  heavens, 
indicating  the  exact  place  of  every  star  down  to  the 
tenth  magnitude.  On  the  evening  of  the  very  day  .upon 
which  this  letter  was  received  (September  23),  Galle 
found  near  the  place  computed  by  Le  Verrier,  a  star  of 
the  eighth  magnitude,  not  contained  on  the  Berlin  chart. 
Its  place  was  carefully  measured  ;  and  the  observations 
being  repeated  on  the  succeeding  evening,  showed  a 
motion  of  more  than  a  minute  of  space.  The  new  star 
was  found  in  longitude  325°  52' ;  the  place  of  the  planet 
computed  by  Le  Verrier  was  324°  58' ;  so  that  this  body 
was  within  one  degree  of  the  computed  point.  Its 
diameter  measured  nearly  three  seconds.  A  coincidence 
so  exact,  left  no  doubt  that  this  was  really  the  body 
whose  effects  had  been  detected  in  the  motions  of 
Uranus.  Mr.  Galle  accordingly  writes  to  Le  Verrier, 
"  the  planet  whose  position  you  marked  out  actually  exists." 
The  news  of  the  discovery  spread  rapidly  over  Europe. 
The  planet  was  observed  at  Gottingen  on  the  27th  of 


THE  PLANET   NEPTUNE.  23 

September,  at  Altona  and  Hamburg  on  the  28th,  and 
at  London  on  the  30th. 

We  must  now  return  to  Professor  Challis,  whom  we 
left  exploring  a  large  zone  of  the  heavens,  and  re- 
cording the  exact  position  of  every  star  down  to  the 
eleventh  magnitude.  These  observations  were  continued 
from  the  29th  of  July  to  the  29th  of  September,  during 
which  time  he  had  made  more  than  three  thousand 
observations  of  stars.  On  the  29th  of  September,  Pro- 
fessor Challis  saw  for  the  first  time  Le  Yerrier's  memoir 
communicated  to  the  Academy  August  31st.  Struck 
with  the  confidence  which  Le  Yerrier  manifested  in  his 
own  conclusions,  Professor  Challis  immediately  changed 
his  mode  of  observation,  and  endeavored  to  distinguish 
the  planet  from  the  fixed  stars  by  means  of  its  disc.  On 
the  same  evening  he  swept  over  the  zone  marked  out 
by  Le  Yerrier,  paying  particular  attention  to  the  phys- 
ical appearance  of  the  brighter  stars.  Out  of  three  hun- 
dred stars,  whose  positions  were  recorded  that  night,  he 
selected  one  which  appeared  to  have  a  disc,  and  which 
proved  to  be  the  planet.  On  the  first  of  October  he 
heard  of  the  discovery  at  Berlin  ;  and  now,  on  comparing 
his  numerous  observations,  he  finds  that  he  had  twice 
observed  the  planet  before,  viz.,  on  August  4th  and 
12th ;  but  he  lost  the  opportunity  of  being  first  to  an- 
nounce the  discovery,  by  deferring  too  long  the  discus- 
sion of  his  observations. 

The  news  of  this  capital  discovery  was  brought  to  this 
country  by  the  steamer  of  October  4th,  and  every  tele- 


24:  HISTORY    OF  ASTRONOMY. 

scope  was  immediately  turned  upon  the  planet.  It  was 
observed  at  Cambridge  by  Mr.  Bond,  October  21st;  it 
was  seen  at  Washington  October  23d,  and  was  regularly 
observed  there  till  January  27th,  when  it  approached 
too  near  the  sun  to  be  longer  followed. 

Le  Terrier,  although  quite  a  young  man,  thus  estab- 
lished at  once  an  enviable  reputation.  He  was  literally 
overwhelmed  with  honors  received  from  the  sovereigns 
and  academies  of  Europe.  He  was  created  an  officer  of 
the  Legion  of  Honor  by  the  King  of  France,  and  a 
special  chair  of  Celestial  Mechanics  was  established  for 
him  at  the  Faculty  of  Sciences.  From  the  King  of  Den- 
mark he  received  the  title  of  Commander  of  the  Koyal 
Order  of  Dannebroga ;  and  the  Eoyal  Society  of  London 
conferred  on  him  the  Copley  medal.  The  Academy  of 
St.  Petersburg  resolved  to  offer  him  the  first  vacancy 
in  their  body ;  and  tlje  Eoyal  Society  of  Grottingen 
elected  him  to  the  rank  of  Foreign  Associate. 

Thus  were  the  predictions  of  Adams  and  Le  Terrier, 
with  regard  to  the  direction  of  the  planet,  at  the  present 
time,  wonderfully  fulfilled ;  but  the  observations  of  a  few 
weeks  sufficed  to  show  that  this  body  was  not  pursuing 
the  orbit  which  these  mathematicians  had  prescribed  for 
it.  Elements  founded  upon  the  hypothesis  of  a  circular 
orbit  were  computed  within  the  first  month  by  Adams, 
Galle,  and  Binet.  These  agreed  very  nearly  with  one 
another,  and  coincided  especially  in  showing  the  distance 
from  the  sun  to  be  about  30.  M.  Talz;  of  the  Mar- 
seilles observatory,  endeavored,  early  in  the  year  1847, 


THE   PLANET   NEPTUNE.  25 

to  deduce  the  form  of  the  orbit  from  the  small  arc 
described  by  the  planet  since  its  discovery,  but  he  found 
himself  unable  to  obtain  a  reliable  value  for  the  eccen- 
tricity. It  became  now  a  question  of  the  greatest  in- 
terest to  determine  with  precision  the  elliptic  elements 
of  the  planet.  This,  however,  was  an  object  of  unusual 
difficulty,  on  account  of  the  slow  motion  of  the  planet, 
its  heliocentric  motion  amounting  to  only  about  two 
degrees  in  a  year.  The  result  derived  from  observations 
embraced  within  a  short  interval  of  time  must  therefore 
be  received  with  great  distrust,  since  a  slight  error  in 
the  measurement  of  a  minute  portion  of  the  orbit  leads 
to  a  much  larger  error  in  the  computed  length  of  the 
remainder  of  the  path.  To  furnish  the  orbit  with  much 
precision,  we  must  have  observations  extending  over  a 
long  series  of  years.  Under  these  circumstances,  it  be- 
came a  question  of  the  highest  interest,  whether  this 
body  may  not  have  been  observed  by  astronomers  of 
former  years,  and  mistaken  for  a  fixed  star.  If  we  could 
obtain  one  good  observation,  made  some  time  in  the 
last  century,  it  would  enable  us  at  once  to  determine  the 
orbit  with  nearly  the  same  precision  as  that  of  Jupiter 
itself.  It  will  then  be  presumed  that  astronomers  have 
not  neglected  to  explore  the  records  of  the  past,  to  dis- 
cover if  possible  some  chance  observation  of  the  new 
planet. 

Mr.  Hind,  of  London,  adopting  the  predicted  elements 
of  Le  Terrier,  examined  Lalande's  and  other  observations 
for  this  purpose,  and  satisfied  himself  that  the  new  planet 


26  HISTORY   OF  ASTRONOMY. 

was  not  there  to  be  found.  An  American  astronomer, 
Mr.  Sears  C.  "Walker,  was  more  fortunate.  Mr.  Walker 
proceeded  in  the  following  manner.  He  first  computed 
the  orbit  which  best  represented  all  the  observations 
which  had  been  made  at  the  "Washington  observatory, 
as  well  as  those  which  had  been  received  from  Europe. 
He  then  computed  the  planet's  probable  place  for  a  long 
series  of  preceding  years,  and  sought  among  the  records 
of  astronomers  for  observations  of  stars  in  the  neighbor- 
hood of  the  computed  path.  Bradley,  Mayer,  and  La- 
caille  have  left  us  an  immense  collection  of  observations, 
yet  they  seldom  recorded  stars  so  small  as  the  body  in 
question.  Among  the  observations  of  Piazzi,  no  one 
was  found  which  could  be  identified  with  the  planet. 
The  Madras  observations  were  generally  confined  to  the 
stars  of  Piazzi's  catalogue.  The  Paramatta  catalogue 
seldom  extends  north  of  the  thirty -third  parallel  of  south 
declination ;  and  Bessel,  in  preparing  his  zones  of 
75,000  stars,  did  not  sweep  far  enough  south  to  com- 
prehend the  planet.  The  only  remaining  chance  of 
finding  an  observation  of  the  planet  was  among  the 
observations  of  Lalande.  The  Histoire  Celeste  Frangaise 
embraces  50,000  stars,  and  Mr.  Walker  soon  found  that 
Lalande  had  swept  over  the  supposed  path  of  the  planet 
on  the  8th  and  10th  of  May,  1795.  He  accordingly 
computed  more  carefully  the  place  of  the  planet  for  this 
period,  making  small  variations  in  the  elements  of  the 
orbit,  so  as  to  include  the  entire  region  within  which  the 
planet  could  possibly  have  been  comprised.  He  then 


THE  PLANET  NEPTUNE.  27 

selected  from  the  Histoire  Celeste  all  the  stars  within  a 
degree  of  the  computed  path.  These  stars  were  nine 
in  number,  of  which  six  had,  however,  been  subse- 
quently observed  by  Bessel,  and  of  course  were  to  be 
set  down  as  fixed  stars.  But  three  stars  remained  which, 
required  special  examination ;  and  of  these,  one  was  too 
small  to  be  mistaken  for  the  planet,  and  a  second  was 
thought  to  be  too  far  from  the  computed  place.  The 
remaining  star  was  distant  only  two  minutes  from  the 
computed  place  of  the  planet ;  it  was  of  the  same  mag- 
nitude, and  was  not  to  be  found  in  Bessel's  observations, 
although  this  part  of  the  heavens  must  have  been  in- 
cluded in  the  field  of  his  telescope.  This  discovery  was 
made  on  the  2d  of  February,  1847;  and  on  the  first 
clear  subsequent  evening,  February  4th,  the  great  equa- 
torial of  the  Washington  observatory  was  pointed  to  the 
heavens,  and  this  star  was  missing.  Where  Lalande,  in 
1795,  saw  a  star  of  the  ninth  magnitude,  there  remained 
only  a  blank.  The  conclusion  seemed  almost  certain, 
that  Mr.  Walker  had  here  obtained  the  object  of  his 
search.  He  accordingly  computed  the  path  upon  this 
supposition,  and  found  that  a  single  elliptic  orbit  would 
represent,  with  almost  mathematical  precision,  the  ob- 
servation of  1795,  and  all  the  observations  of  1846. 

The  case  seemed  completely  made  out.  But  there  was 
a  weak  point  in  tfie  argument.  Lalande  had  marked  his 
observation  of  the  altitude  of  this  star  as  doubtful.  Could 
we  rest  the  decision  of  a  question  so  important  upon  a  bad 
observation?  How  unfortunate,  that  among  the  50,000 


28  HISTOKY  OF  ASTEOKOMY. 

stars  contained  in  this  precious  collection,  there  was 
only  one  which  could  be  presumed  to  have  been  the 
planet,  and  this  observation  the  author  had  marked  as 
doubtful!  Thus  the  question  stood — astronomers  were 
afraid  to  admit,  and  still  could  not  reject  the  conclusions 
of  Mr.  "Walker.  The  steamer  which  left  Boston  on  the 
1st  of  March,  carried  a  copy  of  the  Boston  Courier,  con- 
taining the  account  of  Mr.  Walker's  researches.  This 
paper  was  destined  for  M.  Le  Yerrier ;  and,  on  the  very 
day  of  its  arrival,  he  also  received  a  letter  from  Altona, 
dated  March  21st,  announcing  that  M.  Peteraen  had  dis- 
covered that  this  very  star,  observed  by  Lalande  in 
1795,  was  now  missing  from  the  heavens.  M.  Petersen's 
discovery  was  made  on  the  17th  of  March.  Mr.  Walker 
made  the  same  discovery,  theoretically,  February  2d ; 
and  it  was  confirmed  by  an  actual  inspection  of  the 
heavens,  February  4th.  Mr.  Walker,  then,  has  the  pri- 
ority of  six  weeJcs  in  the  discovery.  Fortunately,  the 
original  manuscripts  of  Lalande  had  been  preserved,  and 
were  deposited  in  the  observatory  of  Paris.  On  con- 
sulting them  it  was  found  that  the  doubtful  mark  ap- 
pended to  the  published  observations,  did  not  exist  in 
the  manuscript.  Moreover,  the  star  had  been  twice  ob- 
served, viz.,  on  the  8th  and  10th  of  May,  1795 ;  but  as 
the  two  observations  did  not  agree,  Lalande  suppressed 
the  former,  and  in  his  printed  book  marked  the  latter 
doubtful.  The  discrepancy  between  the  two  observa- 
tions is  almost  exactly  that  which  is  due  to  two  days' 


THE  PLANET   NEPTUNE;  29 

motion  of  the  planet,  according  to  the  orbit  of  Mr. 
Walker. 

Thus,  then,  we  have  most  unexpectedly  secured  two 
good  observations  in  place  of  one  doubtful  one.  We  can  no 
longer  withhold  our  full  belief.  A  single  elliptic  orbit 
represents  with  great  precision  the  two  observations 
of  Lalande,  and  all  the  observations  subsequently 
made. 

More  recently  it  has  been  announced  that  Dr.  Lamont, 
of  Munich,  had  twice  observed  the  planet  Neptune  as 
a  fixed  star  in  his  zones;  the  first  time  October  25th, 
1845,  when  he  estimated  it  as  of  the  ninth  magnitude ; 
the  second  time  was  September  7th,  1846,  when  it  was 
entered  as  of  the  eighth  magnitude.  The  following,  then, 
are  the  dates  of  the  seven  earliest  observations  of  this 
planet,  so  far  as  at  present  known : 


1795, 

May    8th, 

by  Lalande. 

1795, 

11      10th, 

by  Lalande. 

1845, 

Oct.  25th, 

by  Lamont. 

1846, 

Aug.   4th, 

by  Challis. 

1846, 

"     12th, 

by  Challis. 

1846, 

Sept.    7th, 

by  Lamont. 

1846, 

"      23d, 

by  Galle. 

Let  us  now  compare  the  predicted  orbits  of  Adams 
and  Le  Verrier  with  the  true  orbit  according  to  Mr. 
Walker,  and  the  mass  of  the  planet  as  deduced  from 


30 


HISTORY  OF  ASTRONOMY. 


Lassell's  observations  of  the  satellite.     The  comparison 
stands  as  follows : 


ADAMS. 

LE  VERRIER. 

WALKER. 

Long,  of  the  perihelion, 

299°  11' 

284°  45' 

47°  14'  37" 

Long,  of  ascending  node, 

unknown. 

156     0 

130     6  51 

Inclination  of  the  orbit, 

unknown. 

6     0 

1     46  59 

Mean  long.,  Jan.  1,  1847, 

323  24 

318     47 

328     32  44 

True  long.,  Jan.  1,  1847, 

329  57 

326     32 

327     33  47 

Eccentricity, 

0.120615 

0.10761 

0.00871946 

Mean  distance  from  sun, 

37.25 

36.154 

30.03666 

Time  of  revolution  in  yrs., 

227.323 

217.387 

164.6181 

Mean  daily  motion, 

15".609 

16".318 

21".55448 

Mass, 

efc-Ve" 

WO-Q- 

TT5Q-0- 

In  order  to  render  the  comparison   more   striking,  I 
have  represented  on  the   annexed  figure  the  orbits  of 


THE   PLANET  NEPTUNE.  31 

Le  Verrier  and  Walker.  The  orbits  of  Adams  and  Le 
Yerrier  are  almost  identical,  but  both  differ  materially 
from  Mr.  Walker ;  that  is,  we  are  compelled  to  admit 
that  they  differ  considerably  from  the  truth.  They  rep- 
resent remarkably  well  the  direction  in  which  the  planet 
is  now  seen  from  the  earth,  but  they  give  its  distance 
too  great  by  three  hundred  millions  of  miles  ;  and  in  1690, 
the  planet  Neptune  was  more  than  four  thousand  millions 
of  miles  distant  from  the  place  assigned  by  Le  Verrier  to 
his  planet,  and  differed  nearly  a  quadrant  from  it  in 
direction.  This  discrepancy  is  so  great  as  to  have  given 
occasion  for  the  remark,  that  the  planet  actually  dis- 
covered is  not  the  planet  predicted  by  Le  Verrier.  What 
reason  there  may  be  for  this  remark  I  shall  consider 
hereafter. 

Some  difficulty  at  first  occurred  in  deciding  upon  a 
name  for  the  new  planet.  The  Bureau  des  Longitudes 
of  Paris  were  in  favor  of  calling  it  Neptune,  and  this 
name  was  given  out  by  Le  Yerrier  in  private  letters 
to  different  astronomers  in  England  and  Germany.  Sub- 
sequently, Le  Yerrier  commissioned  his  friend  Arago  to 
give  the  planet  a  name ;  and  Arago  declared  he  would 
never  call  it  by  any  other  name  than  Le  Verrier.  When 
Sir  William  Herschel  discovered  a  planet,  he  named  it 
Georgium  Sidus ;  and  the  name  of  "  the  Georgian"  was 
retained  until  recently  in  the  English  Nautical  Almanac. 
But  this  name  being  offensive  to  the  national  pride  of  the 
French,  they  at  first  called  the  planet  Herschel,  and  after- 
ward Uranus.  The  latter  name  has  now  come  into  exclu- 


32  THE  PLANET   NEPTUNE. 

sive  use ;  but  Arago,  in  order  to  secure  an  honor  to  his 
friend  Le  Verrier,  proposed  to  restore  the  name  Herschel, 
and  also,  that  each  of  the  smaller  planets  should  receive 
the  name  of  its  discoverer. 

The  astronomers  of  Europe  refused  to  concur  in  the 
decision  of  Arago.  There  are  objections  to  this  prin- 
ciple of  nomenclature,  some  of  which  have  considerable 
weight.  The  name  of  the  discoverer  of  a  planet  may 
happen  to  be  immoderately  long,  or  ludicrously  short, 
difficult  to  pronounce,  or  comically  significant.  Then, 
also,  if  the  same  astronomer  should  be  fortunate  enough 
to  discover  more  than  one  planet,  we  should  be  obliged 
to  repeat  the  surname  with  a  prefix.  Already  we  have 
two  planets  discovered  by  Olbers;  two  discovered  by 
Hencke,  ten  by  Hind,  seven  by  Gasparis,  five  by  Luther, 
four  by  Groldschmidt,  and  five  by  Chacornac. 

Moreover,  it  often  happens  that  several  persons  con- 
tribute an  important  part  in  the  discovery  of  the  same 
body.  Thus  the  planet  Ceres  was  first  discovered  by 
Piazzi,  in  the  course  of  a  series  of  observations  having 
a  different  object  in  view.  After  a  few  weeks,  the  planet 
became  invisible  from  its  proximity  to  the  sun.  As- 
tronomers computed  the  orbit  from  Piazzi's  observations, 
and  searched  for  it  some  months  afterward,  when  it  ought 
again  to  have  come  into  view.  But  the  planet  could  not 
be  found.  Ceres  was  entirely  lost,  and  would  not  have 
been  seen  again,  had  not  Grauss,  by  methods  of  his  own 
invention,  computed  a  much  more  accurate  orbit,  which 
disclosed  the  exact  place  of  the  fugitive,  and  enabled 


THE  PLANET  NEPTUNE,  33 

De  Zach  to  find  it  immediately  upon  pointing  his  tel- 
escope to  the  heavens.  To  Gauss,  therefore,  belongs 
the  honor  of  being  the  second  discoverer  of  Ceres ;  and 
the  second  discovery  was  far  more  glorious  than  the  first. 
The  discovery  of  the  new  planet  has  been  justly 
characterized  by  Professor  Airy  as  "  the  effect  of  a  move- 
ment of  the  age"  The  honor  of  the  discovery  is  not  to 
be  exclusively  engrossed  by  either  Adams  or  Le  Terrier. 
The  labors  of  numerous  astronomers  had  prepared  the 
way,  and  contributed  more  or  less  directly  to  the  dis- 
covery. An  eminent  critic  has  ridiculed  this  idea.  But 
Mr.  Adams  himself  informs  us,  that  his  attention  was 
first  directed  to  the  subject  of  the  motions  of  Uranus, 
by  reading  Airy's  report  on  the  recent  progress  of  as- 
tronomy ;  and  Le  Yerrier  states,  that  in  the  summer  of 
1845,  he  suspended  the  researches  on  comets,  upon 
which  he  was  then  employed,  to  devote  his  time  to 
Uranus,  at  the  urgent  solicitation  of  M.  Arago.  Omitting 
several  who  have  indirectly  contributed  to  this  result, 
we  find  four  whose  names  will  ever  be  honorably  asso- 
ciated with  the  discovery  of  the  planet  Neptune,  viz., 
Adams,  Challis,  Le  Yerrier,  and  Galle.  Adams  first  de- 
termined the  approximate  place  of  the  new  planet  from 
the  perturbations  of  Uranus.  Professor  Challis  was  the 
first  to  institute  a  systematic  search  for  the  planet,  and 
had  actually  secured  two  observations  of  it  before  it  was 
seen  at  Berlin.  True,  he  did  not  at  the  time  know  that 
he  had  found  the  planet,  for  he  had  not  interrogated  his 

observations.     But  the  prize  was  secured,  and  he  would 

2*    i 


84  HISTORY  OF  ASTRONOMY. 

infallibly  have  recognized  it  as  soon  as  he  had  instituted 
a  comparison  of  his  observations.  Being  fully  resolved  to 
make  sure  of  the  diamond,  he  shoveled  up  with  it  a 
great  mass  of  rubbish,  and  stored  it  all  away  to  examine 
at  his  leisure. 

To  Le  Yerrier  belongs  the  credit  of  having  been  the 
first  to  publish  to  the  world  the  process  by  which  he 
arrived  at  the  conclusion  of  the  existence  of  a  new 
planet;  and  it  is  conceded  that  his  researches  were 
more  complete  and  elaborate  than  those  of  his  rival; 
while  to  Galle  belongs  the  undisputed  honor  of  having 
been  the  first  practically  to  recognize  this  body  as  a 
planet. 

To  give  to  the  new  planet  the  name  of  Le  Yerrier, 
would  be  indeed  to  confer  honor  where  honor  was  due ; 
but  it  would  be  dishonor  to  others  whose  pretensions  are 
but  little  inferior  to  his  own.  The  astronomers  of  Eu- 
rope have  preferred  to  take  a  name  from  the  divinities 
of  the  Eoman  mythology,  in  conformity  with  a  well- 
established  usage;  and  as  the  name  of  Neptune  har- 
monizes with  this  system,  and  withal  was  first  suggested 
by  the  Bureau  des  Longitudes,  they  decided  to  adhere 
to  it.  This  was  the  unanimous  voice  of  Europe,  with 
the  exception  of  France,  and  the  astronomers  of  France 
have  since  acquiesced  in  this  decision. 

The  discovery  of  Neptune  has  given  an  unequivocal 
refutation  to  Bode's  law  of  the  planetary  distances.  This 
famous  law  may  be  thus  stated.  If  we  set  down  the 
number  4  several  times  in  a  row,  and  to  the  second  4 


THE   PLANET  NEPTUNE. 


35 


add  3,  to  the  third  4  add  twice  3  or  6,  to  the  next  4  add 
twice  6  or  12,  and  so  on,  as  in  the  following  table,  the 
resulting  numbers  will  represent  nearly  the  relative 
distances  of  the  planets  from  the  sun : 

444 
3        6 

4       7     lO 


4 
12 

16 


4 
24 

28 


4,  etc. 
48,  etc. 

52,  etc. 

If  the  distance  of  the  earth  from  the  sun  be  called  10, 
then  4  will  represent  nearly  the  distance  of  Mercury ;  7 
that  of  Venus ;  and  so  of  the  rest.  This  law  was  never 
accurately  verified  in  the  case  of  any  of  the  planets,  and 
Neptune  forms  a  decided  exception  to  it.  This  fact  is 
exhibited  more  clearly  in  the  following  table,  which 
shows  first  the  true  relative  distance  of  each  of  the 
planets;  secondly,  the  distance  according  to  Bode's  law, 
and  thirdly,  the  error  of  this  law : 


True 
distance. 

Bode'  s 
law. 

Error. 

True 
distance- 

Bode's 
law. 

Error. 

Mercury, 

3-87 

4 

0-13 

Jupiter, 

52-03 

52 

0-03 

Venus, 

7-23 

7 

0-23 

Saturn, 

95-39 

100 

4-61 

Earth, 

10-00 

10 

Uranus, 

191-82 

196 

4-18 

Mars, 

15-24 

16 

0-76 

Neptune, 

300-36 

388 

87-64 

40  Asteroids 

26-09 

28 

1-91 

It  will  be  seen  from  this  table,  that '  although  this  law 
represents  pretty  well  the  distances  of  the  nearer  planets, 
the  error  is  quite  large  for  Saturn  and  Uranus ;  and  for 
Neptune  the  error  is  altogether  overwhelming,  amount- 
ing to  more  than  eight  hundred  millions  of  miles,  a  quan- 
tity almost  equal  to  the  distance  of  Saturn  from  the  sun. 
It  is  mere  mockery  to  dignify  such  coincidences  with 


36  HISTORY  OF  ASTRONOMY. 

the  name  of  a  law.  A  law  of  nature  is  precise — it  is 
capable  of  exact  numerical  application.  Let,  then,  the 
preceding  rule  be  called  the  law  of  Bode ;  it  is  not  a  law 
of  nature. 

It  was  at  first  the  opinion  of  some  observers,  that 
Neptune  is  surrounded  by  a  ring  like  Saturn.  Mr.  Las- 
sell,  of  Liverpool,  has  an  excellent  Newtonian  reflector 
of  twenty  feet  focal  length,  and  two  feet  aperture,  with 
which  he  has  made  numerous  observations  of  the  planet. 
On  the  3d  of  October,  1846,  he  was  struck  with  the 
shape  of  the  planet,  as  being  not  that  of  a  round  ball ; 
and  again,  on  the  10th  of  October,  he  received  a  distinct 
impression  that  the  planet  was  surrounded  by  an  ob- 
liquely situated  ring.  On  the  10th  of  November  the 
planet  appeared  very  much  like  Saturn,  as  seen  with  a 
small  telescope,  and  low  power,  though  much  fainter. 
Several  other  persons  also  saw  the  supposed  ring,  and 
all  in  the  same  direction.  During  the  season  of  1847, 
Mr.  Lassell  frequently  saw  the  same  appearance  again, 
and  found  its  angle  of  position  to  be  70  degrees  S.  W. 
He  also  satisfied  himself  that  this  appearance  did  not 
arise  from  any  defect  in  his  telescope. 

Professor  Challis  states  that  on  the  12th  of  January, 
1847,  he  received  for  the  first  time  a  distinct  impression 
that  the  planet  was  surrounded  by  a  ring.  Two  inde- 
pendent drawings,  made  by  himself  and  his  assistant, 
gave  the  annexed  representation  of  its  appear- 
ance. On  the  14th,  he  saw  the  ring  again,  and 
was  surprised  that  he  had  not  noticed  it  in  his 


THE    PLANET   NEPTUNE.  37 

earlier  observations.  The  ratio  of  the  diameter  of  the 
ring  to  that  of  the  planet,  was  about  that  of  three 
to  two. 

On  the  other  hand,  the  great  telescope  at  Cambridge, 
Mass.,  shows  no  ring.  The  following  is  the  testimony 
of  the  director,  Mr.  W.  C.  Bond.  "  We  are  satisfied  that 
there  is  not  at  present  visible  any  ring  surrounding 
Neptune  within  the  reach  of  the  Cambridge  telescope. 
Both  my  son  George  and  myself  have  repeatedly  had 
opportunities  of  examining  the  planet  under  high  powers 
with  the  full  aperture  of  fifteen  inches,  and  have  seen 
only  a  round  disc,  while  our  micrometrical  measures  of 
his  diameter  agreed  well  together." 

Mr.  Lassell's  present  opinion  appears  to  be  less  in 
favor  of  a  ring  than  formerly.  Yet,  on  the  29th  of 
August,  1851,  he  recorded  in  his  journal,  "  I  received 
again  an  impression  of  a  ring-like  appendage,  but  it  is 
principally  on  the  south  side,  and  is  nearly  at  right  angles 
to  a  parallel  of  declination."  Also  on  the  4th  of  Novem- 
ber, 1852,  at  Malta,  in  latitude  35°  53',  under  the  most 
favorable  atmospheric  circumstances,  he  recorded  in  his 
journal,  "  I  receive  a  decided  impression  of  ellipticity  in 
the  direction  of  the  greatest  elongation  of  the  satellite. 
There  is  an  impression  of  an  extremely  flattened  ring  in 
the  direction  of  the  transverse  axis.  I  think  I  have 
never  seen  Neptune  so  well  before."  It  is  understood 
that  the  astronomers  at  Pulkova  have  not  yet  succeeded 
in  observing  any  appearance  such  as  would  lead  to  the 
suspicion  of  a  ring.  Under  these  circumstances,  if  we 


38  HISTORY   OF  ASTRONOMY. 

do  not  entirely  deny  the  possible  existence  of  a  ring,  we 
must  at  least  hold  our  minds  in  suspense,  and  wait 
patiently  for  further  evidence.  It  is  possible  that  this 
question  may  not  be  fully  cleared  up  until  some  more 
powerful  telescope  is  turned  upon  the  planet,  or  it  can 
be  seen  in  a  different  part  of  its  orbit. 

Neptune  is  attended  by  at  least  one  satellite.  Mr.  Las- 
sell  states  that  on  the  10th  of  October,  1846,  he  observed 
a  faint  star,  distant  from  the  planet  about  three  diam- 
eters. On  the  llth  and  30th  of  November,  and  also 
December  3d,  he  saw  a  small  star  having  about  the  same 
appearance ;  and  he  considered  it  probable  that  the  star 
was  a  satellite.  On  the  7th  of  July,  1847,  he  again  saw 
the  supposed  satellite,  and  on  the  following  evening  the 
planet  and  satellite  had  both  changed  their  position  with 
reference  to  the  neighboring  stars.  On  the  22d,  25th, 
and  26th  of  the  same  month,  the  planet  appeared,  at- 
tended by  a  satellite ;  and  on  the  1st  of  August  he  ob- 
tained the  fullest  evidence  of  the  verity  of  the  satellite, 
in  being  able  clearly  to  ascertain,  that  during  the  two 
hours  he  watched  the  planet,  it  had  carried  the  satellite 
along  with  it  in  its  orbital  motion.  On  the  20th  of  Sep- 
tember, 1847,  Mr.  Lassell  announced  that  during  the 
current  year  he  had  obtained  twenty  observations  of  the 
satellite,  and  from  them  all  he  concluded  that  its  time 
of  revolution  was  five  days,  twenty  hours,  and  fifty 
minutes.  Mr.  Bond,  at  Cambridge,  during  the  years 
1847  and  1848,  obtained  repeated  measures  of  the  dis- 
tance and  angle  of  position  of  this  satellite  by  means 


THE  PLANET  NEPTUNE.  39 

of  a  micrometer  with  illuminated  wires.  By  a  com- 
bination of  all  the  Cambridge  observations,  Mr.  Bond 
has  deduced  the  time  of  revolution  five  days  and  twenty- 
one  hours.  A  discussion  of  the  entire  series  of  ob- 
servations made  by  Mr.  Lassell  at  Malta  in  1852,  gives 
the  period  five  days,  twenty-one  hours,  two  minutes  and 
forty-four  seconds,  and  the  motion  of  the  satellite  is 
found  to  be  retrograde.  The  radius  of  its  orbit  is  seven- 
teen seconds,  which  gives  about  236,000  miles  for  the 
distance  of  the  satellite  from  the  planet.  The  light  of 
the  satellite  is  nearly  equivalent  to  that  of  a  star  of  the 
fourteenth  magnitude.  It  is  always  more  brilliant  in 
the  S.  W.  than  in  the  N.  E.  part  of  its  orbit,  present- 
ing, in  this  respect,  a  striking  analogy  with  the  outer 
satellite  of  Saturn.  In  the  former  position,  Mr.  Lassell 
found  it  easy  to  observe,  in  the  latter,  extremely  diffi- 
cult. 


AFPAEENT  OKBIT  OF  THE  SATELLITE  OF  NEPTUNB  FOB  1852. 

The  preceding  results  enable  us  to  compute  the  mass 
of  Neptune,  which  is  found  to  be  TT }^  part  of  the  sun. 

Mr.  Bond  states  that  he  has  at  times  been  quite  con- 
fident of  seeing  a  second  satellite,  but  has  never  yet  been 
able  to  obtain  successive  measures  of  its  distance  from 
the  primary.  Mr.  Lassell  also  in  August,  1850,  sus- 


40  HISTOKY  OF  ASTKONOMY. 

pected  he  saw  a  second  satellite,  but  was  unable  to  follow 
it  long  enough  to  establish  its  character. 

The  grand  question  still  remains  untouched —  Will  the 
new  planet  explain  the  observed  irregularities  in  the  motion  of 
Uranus  ? 

The  planet  having  been  actually  discovered  in  the 
heavens,  by  means  of  certain  predicted  elements,  and 
within  one  degree  of  the  predicted  place,  the  natural  con- 
clusion was,  that  those  elements  were  extremely  near  the 
truth,  and  that  the  planet  would  perfectly  explain  those 
effects  by  whose  study  its  own  existence  had  been  detect- 
ed. When,  however,  observation  had  rendered  it  certain 
that  the  planet  moved  in  a  smaller  and  less  eccentric 
orbit  than  had  been  predicted,  it  became  doubtful 
whether  it  would  account  for  the  anomalies  in  the  mo- 
tion of  Uranus.  When  Le  Yerrier,  in  March,  1847,  re- 
ceived notice  of  the  computations  of  Mr.  Walker,  who 
obtained  an  orbit  differing  but  little  from  a  circle,  he  at 
once  pronounced  the  small  eccentricity  incompatible  with 
the  observed  perturbations.  Mr.  Adams,  in  a  letter  June 
llth,  1847,  says,  "I  am  hard  at  work  on  the  perturba- 
tions of  Uranus,  in  order  to  obtain  a  new  theoretical  de- 
termination of  the  place.  The  general  values  of  the  per- 
turbations are  enormous,  far  exceeding  any  thing  else  of 
the  same  kind  in  the  system  of  the  primary  planets.  A 
comparison  of  the  numerical  expressions  for  the  pertur- 
bations, which  I  have  now  obtained,  with  those  which  I 
used  before,  would  justify  some  skepticism  as  to  former  con- 


THE  PLANET   NEPTUNE.  41 

elusions.     But  we  shall  soon  see  how  this  great  apparent 
difference  affects  the  result." 

By  referring  to  the  table  on  page  30,  it  will  be  seen 
that  Adams  and  Le  Verrier  explain  the  anomalies  of 
Uranus  by  assuming  a  very  large  body  (having  twice  the 
mass  of  Uranus)  moving  in  a  very  eccentric  orbit.  It  is 
now  discovered  that  the  orbit  hardly  differs  at  all  from  a 
circle,  and  that  the  mass  is  scarcely  one  half  of  that  which 
had  been  assumed.  Now  the  more  eccentric  the  orbit, 
the  greater  must  be  the  inequality  of  a  planet's  action 
upon  other  bodies  whose  orbits  are  nearly  circular.  A 
considerable  part  of  the  observed  irregularities  in  the  mo- 
tion of  Uranus,  was  explained  by  Adams  and  Le  Verrier, 
by  means  of  the  great  eccentricity  ascribed  to  their  hypo- 
thetical planet.  This  portion  is  now  gone  with  the  failure 
of  the  eccentricity.  But,  on  the  other  hand,  Neptune  is 
found  to  be  much  nearer  Uranus  than  the  hypothetical 
planet,  and  in  consequence  of  this  proximity,  its  disturb- 
ing action  is  increased,  so  that  these  two  variations  of  the 
elements  partly  compensate  each  other.  The  mass  of 
Neptune  is  also  less  than  the  hypothetical  planet  of  Le 
Verrier,  and  on  this  account  its  disturbing  action  is  dimin- 
ished. To  what  extent  the  planet  Neptune  would  account 
for  the  perturbations  of  Uranus  was  not  determined  until 
1848.  In  a  communication  made  to  the  American  Acad- 
emy April  4,  1848,  Professor  Peirce  announced  that  the 
motions  of  Uranus  are  perfectly  explained,  provided  we 
adopt  Mr.  Walker's  orbit,  and  the  mass  of  Neptune, 
which  is  derived  from  Mr.  Bond's  observations  of  Las- 


42  HISTORY  OF  ASTRONOMY. 

sell's  satellite.  By  his  computations,  the  great  anomalies 
which  had  been  observed,  and  which  are  represented  on 
page  12,  almost  entirely  disappear.  All  the  modern  ob- 
servations are  represented  quite  as  well  as  by  the  theories 
of  Adams  and  Le  Yerrier,  and  the  observation  of  1690 
much  better.  The  error  of  Flamsteed's  observation  of 
1690,  according  to  Adams's  computation,  was  50",  and  ac- 
cording to  Le  Terrier's  computation,  20";  but  according 
to  Peirce's  theory,  this  observation  is  represented  within  a 
single  second. 

So  then  the  anomalies  of  Uranus,  which  had  so  long 
perplexed  astronomers,  are  perfectly  accounted  for.  But 
it  is  obvious,  from  a  glance  at  the  diagram  on  page  30 , 
that  the  planet  actually  discovered  is  moving  in  an  orbit 
considerably  different  from  what  had  been  computed,  so 
that  it  has  been  claimed  by  Professor  Peirce  that  Neptune 
is  not  the  planet  whose  existence  had  been  predicted  by  Le 
Verrier.  Is  this  discrepancy  between  the  observed  and 
predicted  orbits  of  a  serious  nature ;  and  if  so,  how  is  it 
to  be  accounted  for  ?  This  question  has  been  fully  dis- 
cussed by  Le  Yerrier  himself.  Le  Yerrier  attempted  to 
deduce  the  position  of  a  new  planet,  by  studying  the  ir- 
regularities in  the  motion  of  Uranus.  The  data  which 
he  was  obliged  to  employ,  were  liable  to  some  uncertainty. 
This  uncertainty  of  the  data  did  not  result  merely  from 
the  uncertainty  of  the  observations,  but  from  two  other 
causes,  viz.,  a  possible  error  in  the  mass  of  Saturn  suffi- 
cient to  add  3"  to  the  uncertainty  of  the  observations,  and 
from  the  possible  influence  of  a  planet  situated  beyond 


THE  PLANET  NEPTUNE.  43 

Neptune,  whose  action  upon  Uranus  might  easily  amount 
to  5"  or  1".  The  uncertainty  of  the  data  results  from  the 
combination  of  these  three  effects,  and  might  amount  to 
10 ''  or  12",  while  the  uncertainty  of  the  modern  observa- 
tions does  not  exceed  2*  or  3*.  Now  the  irregularities  in 
the  motion  of  Uranus,  which  serve  as  the  basis  of  the  dis- 
cussion, do  not  exceed  at  the  utmost  two  minutes  of 
space,  and  for  the  most  part  they  are  less  than  one 
minute ;  so  that  the  data  were  uncertain  to  one  tenth  of 
their  whole  amount.  Le  Verrier,  therefore,  claims  that  it 
is  unreasonable  to  demand  of  him  a  greater  degree  of  ac- 
curacy in  the  positions  assigned  to  his  computed  planet, 
than  one  tenth  of  their  value,  and  he  has  attempted  to 
show  that  these  positions  are  not  in  error  by  so  large  a 
quantity.  Moreover,  as  he  computes  the  position  of  his 
planet  only  by  means  of  the  disturbance  which  it  causes 
in  the  motion  of  Uranus,  he  can  only  compute  this  posi- 
tion when  this  disturbance  is  appreciable.  Now  this  dis- 
turbance, on  account  of  the  distance  of  the  planets  from 
each  other,  is  inappreciable  from  1690  to  1812.  It  was 
only  from  1812  to  1842,  that  he  was  furnished  with  ob- 
servations in  which  the  disturbing  action  of  Neptune  was 
sensible,  and  the  place  of  the  planet  for  any  other  time 
must  be  deduced  from  its  motion  during  these  30  years. 
He  then  proceeds  to  show  that  the  positions  he  had  as- 
signed to  Neptune  during  this  period,  and  also  for  a 
much  longer  time,  were  not  in  error  by  one  tenth  of  their 
whole  amount.  Let  us  consider, 
I.  The  error  in  the  computed  longitudes  of  Neptune. 


44 


THE  PLANET   NEPTUNE. 


The  following  is  the  comparison  between  Le  Yerrier's 
predicted  places  and  those  resulting  from  Mr.  Walker's 
orbit  during  a  period  of  120  years. 


Year. 

1767 

Predicted 
longitude. 

l74°-3 

Longitude  according 
to  Mr.  Walker. 

155°-5 

Error. 
+  18'°8 

1777 

190-4 

176-7 

+  13-7 

1787 

207-6 

198-0 

+   9-6 

1797 

225-9 

219-3 

+   6-6 

1807 

245-2 

240-7 

+   4-5 

1817 

265-3 

262-2 

+   3-1 

1827 

285-9 

283-9 

+    2-0 

1837 

306-4 

305-7 

+   0-7 

1847 

326-5 

327-5 

—  1-0 

1857 

345-7 

349-7 

—  4-0 

1867 

3-9 

11-6 

—  7-7 

1877 

20-9 

33-6 

—12-7 

1887 

36-9 

55-5 

—  18-6 

Thus,  it  appears,  that  during  a  period  of  120  years, 
the  longitude  of  Neptune,  according  to  Le  Terrier's 
computation,  did  not  differ  from  that  determined  by  Mr. 
"Walker  from  the  observations,  more  than  18°'8,  or  about 
one  twentieth  part  of  an  entire  circumference ;  and  during 
the  period  in  which  the  action  of  Neptune  has  been 
clearly  marked,  that  is,  since  1812,  the  error  of  Le 
Yerrier's  theory  has  not  exceeded  3°'7.  For  1690,  the 
theory  is  indeed  very  much  at  fault,  but  that  is  the 
result  of  a  comparatively  small  error  in  the  positions 
assigned  during  the  present  century. 

II.  The  error  in  the  computed  distance  from  the  sun. 


*      THE  PLANET  NEPTUNE.  45 

The  following  table  shows  the  distance  of  the  planet 
from  the  sun,  as  predicted  by  Le  Terrier,  and  that  de- 
duced from  the  computations  of  Mr.  Walker,  the  dis- 
tance being  expressed  in  radii  of  the  earth's  orbit. 


In  1812 

.rreoicteo. 
distance. 

32-7 

uoservea 
distance. 

30-4' 

Error. 

+  2-3 

1822 

32-3 

30-3 

+  2-0 

1832 

32-6 

30-2 

+  2-4 

1842 

32-8 

30-1 

+  2-7 

Thus  it  appears,  that  during  the  30  years  in  which 
the  action  of  Neptune  upon  Uranus  has  been  sensible, 
the  error  of  the  predicted  distance  from  the  sun  has  never 
amounted  to  one  tenth  of  the  whole  quantity. 

There  appears,  however,  a  discrepancy  between  the 
limits  of  distance  which  Le  Terrier  assigned  to  his  planet 
before  its  discovery,  and  those  which  he  has  since  pub- 
lished. In  1846  he  attempted  to  determine  the  limits 
within  which  the  distance  might  be  supposed  to  vary 
without  involving  an  error  greater  than  5"  in  any  of  the 
observations  since  1781.  He  decided  that  the  mean  dis- 
tance could  not  be  less  than  35*04,  nor  more  than  37*90. 
Now  the  mean  distance  of  Neptune  from  the  sun  is 
known  to  be  only  30*04.  From  these  two  propositions 
the  legitimate  conclusion  would  seem  to  be  that  Neptune 
is  not  the  planet  predicted  by  Le  Terrier.  But  Le  Ter- 
rier has  lately  changed  his  ground,  and  he  has  dis- 
covered that  without  supposing  the  uncertainty  of  the 
modern  data  to  exceed  5",  the  theory  of  Uranus  may  be 
satisfied  by  a  planet  situated  in  1846  at  any  distance  from 


46  HISTORY  OF  ASTRONOMY.   ' 

the  sun  between  29*6  and  35'2.  It  is  not  obvious  how 
this  last  statement  can  be  reconciled  with  the  limits 
published  in  1846.  Doubtless  Le  Yerrier  has  discovered 
that  the  limits  which  he  first  assigned  were  erroneous. 
If  we  compare  the  predicted  mean  distance  with  that 
deduced  from  the  observations,  we  shall  find  the  error 
of  the  former  to  amount  to  one  fifth  of  the  whole 
quantity. 

III.  The  error  in  the  eccentricity  of  Neptune. 

Le  Yerrier  assigned  to  the  orbit  of  his  planet  an  ec- 
centricity of  0'1076;  the  computations  of  Mr.  Walker 
make  the  eccentricity  of  Neptune  0*0087. 

The  discrepancy  is  considerable ;  but  Le  Yerrier  states 
that  if  we  admit  an  uncertainty  of  5"  only  in  the  modern 
data,  the  eccentricity  of  the  body  producing  the  irreg- 
ularities of  Uranus  may  be  chosen  arbitrarily  between 
0*2031  and  0'0592 ;  and  if  we  admit  an  uncertainty  of 
7"  or  8"  in  the  modern  data,  the  eccentricity  may  have 
any  value  between  0*25  and  zero.  Professor  Peirce  has 
shown  that  the  planet  Neptune,  with  an  eccentricity 
almost  zero,  reconciles  all  the  modern  observations  of 
Uranus  within  3". 

IY.  Error  of  the  computed  mass  of  Neptune. 

The  mass  assigned  by  Le  Yerrier  to  his  predicted 
planet  was  -g-^Vo  °f  the  sun's  mass ;  but  he  adds,  that  if 
we  admit  an  uncertainty  of  5"  in  the  data,  this  mass  may 
have  any  value  between  TTVo-  and  TT^O--  The  mass  of 
Neptune  deduced  by  Struve,  from  his  own  observations 
of  the  satellite,  is  744-94 ;  but  the  mass  deduced  from  Las- 


THE  PLANET  NEPTUNE.  47 

sell's  observations,  is  TT!O-O--  The  former  value  comes 
fairly  within  the  limits  assigned  by  Le  Terrier,  the  latter 
somewhat  exceeds  them. 

On  the  whole,  we  must  conclude  that  the  orbit  of  Nep- 
tune agrees  with  the  orbit  predicted  by  Le  Yerrier,  very 
nearly  within  the  limits  which  Le  Yerrier  now  assigns, 
upon  the  supposition  of  an  uncertainty  of  5'  in  the  data 
since  1781.  But  these  limits,  with  respect  to  distance 
and  time  of  revolution,  are  very  different  from  those  as- 
signed before  the  discovery  of  the  planet.  The  orbit  of 
Neptune  is  not  included  within  the  limits  which  Le  Yer- 
rier then  assigned ;  and  it  is  a  legitimate  inference,  from 
his  own  premises,  that  Neptune  is  not  the  planet  whose 
existence  he  announced. 

It  should  also  be  borne  in  mind  that  Professor  Peirce 
has  shown  that  Neptune  reconciles  all  the  observations 
of  Uranus  since  1781  within  3",  and  that  the  greatest  error 
of  any  of  the  ancient  observations  according  to  his  theory 
is  8" ;  thus  proving  that  Le  Yerrier's  suspicion  of  the  ex- 
istence of  a  planet  beyond  Neptune,  and  of  an  error  in 
the  mass  of  Saturn  is  unfounded.  The  data,  therefore, 
instead  of  being  uncertain  to  one  tenth  of  their  whole 
amount,  were  generally  reliable  within  one  sixtieth  of 
their  value ;  and  Le  Yerrier's  elements  are  erroneous 
to  an  extent  far  beyond  the  one  sixtieth  of  their  value. 

It  will  naturally  be  asked,  how  has  it  happened  that 
two  astronomers,  Adams  and  Le  Yerrier,  have  arrived, 
by  independent  computations,  at  almost  identically  the 
same  result,  and  have  made  such  mistakes  with  respect 


48  HISTOEY  OF  ASTRONOMY. 

to  the  mean  distance,  eccentricity,  and  mass  of  the  planet? 
The  answer  is  plain :  they  were  misled  by  placing  too 
great  confidence  in  Bode's  law  of  the  planetary  distances. 
Since  it  was  necessary,  in  the  first  instance,  to  make  some 
hypothesis  with  regard  to  the  distance  of  the  disturbing 
body  from  the  sun,  both  computers  started  with  that  sup- 
position which  was  generally  thought  most  probable. 
The  distance  of  Saturn  from  the  sun  is  nearly  double 
that  of  Jupiter  ;  the  distance  of  Uranus  is  almost  exactly 
double  that  of  Saturn  ;  hence  it  seemed  probable  that  the 
planet  they  were  in  search  of,  would  be  found  at  a  dis- 
tance about  double  that  of  Uranus.  Accordingly  this  as- 
sumption was  made  the  basis  of  their  first  computations ; 
but  neither  of  the  computers  accepted  this  as  his  final  re- 
sult, without  attempting  to  verify  it.  They  both  varied 
the  assumed  distance,  and  found  that  by  bringing  the 
planet  a  little  nearer  the  sun,  the  observed  irregularities 
of  Uranus  were  still  better  explained.  The  distance  of 
36*154  (or  about  3435  millions  of  miles),  finally  adopted 
by  Le  Yerrier,  was  that  which  appeared  to  reconcile  all 
the  observations  most  satisfactorily.  This  distance  corre- 
sponds to  a  period  of  two  hundred  and  seventeen  years. 
Le  Yerrier  found  (or  thought  he  found)  that  whether  he 
increased  or  diminished  this  distance,  the  observations  of 
Uranus  were  not  so  well  represented.  He  hence  inferred 
that  the  mean  distance  from  the  sun  could  not  be  less 
than  35*04,  nor  greater  than  37*90.  (Le  demi-grand  axe 
de  1'orbite  ne  pent  varier  qu'entre  les  limites  35*04  et. 
37*90.)  The  periods  of  revolution  corresponding  to  these 


THE  PLANET  NEPTUNE.  49 

distances  are  about  207  and  233  years.  This  conclusion 
was  unauthorized,  and  is  now  admitted  by  Le  Verrier  to 
have  been  erroneous.  The  mean  distance  of  Neptune 
from  the  sun  is  only  thirty  times  that  of  the  earth,  and 
still  it  explains  the  motions  of  Uranus  even  better  than 
the  hypothetical  planet  of  Le  Verrier. 

Professor  Peirce  has  shown  that  an  important  change 
in  the  character  of  the  perturbations  takes  place  near  the 
distance  35*3.  A  planet  at  the  distance  35'3  would  re- 
volve about  the  sun  in  210  years,  which  is  exactly  two 
and  a  half  times  the  period  of  the  revolution  of  Uranus, 
Now  if  the  times  of  revolution  of  two  planets  were  ex- 
actly as  2  to  5,  the  effects  of  their  mutual  influence  would 
be  peculiar  and  complicated.  This  distance  of  35*3  is  a 
complete  barrier  to  any  logical  deduction,  and  the  invest- 
igations with  regard  to  the  outer  space  can  not  be  ex- 
tended to  the  interior. 

The  observed  distance  30  belongs  to  a  region  which  is 
even  more  interesting  in  reference  to  Uranus  than  that  of 
35 '3.  The  time  of  revolution  which  corresponds  to  the 
mean  distance  30*4  is  168  years,  being  exactly  double  the 
year  of  Uranus ;  and  the  influence  of  a  mass  revolving  in 
this  time  would  give  rise  to  very  singular  and  marked 
irregularities  in  the  motion  of  this  planet.  Professor 
Peirce  was  hence  led  to  the  conclusion  that  the  planet 
Neptune  was  hot  the  planet  to  which  geometrical  analysis 
had  directed  the  telescope  ;  that  its  orbit  was  not  contain- 
ed within  the  limits  of  space  explored  by  Adams  and  Le 

Verrier  in  searching  for  the  source  of  the  disturbances  of 

3 


50  HISTORY  OF  ASTRONOMY. 

Uranus ;  and  that  its  discovery  by  Galle  must  be  regarded 
as  a  nappy  accident.  Besides  that  solution  of  the  prob- 
lem which  Le  Yerrier  and  Adams  obtained,  there  is 
another  solution  which  corresponds  to  the  orbit  and  mass 
of  Neptune.  The  fact  however  that  Neptune  does  not 
correspond  to  Le  Verrier's  solution  can  not  detract  from 
the  merit  or  value  of  his  investigation.  Since,  by  using 
all  the  observations  within  his  reach,  he  found  an  orbit 
and  mass  capable  of  accounting  for  the  observed  motions 
of  Uranus,  he  is  entitled  in  the  opinion  of  mathematicians 
to  all  the  admiration  he  would  have  received  had  such  a 
planet  actually  moved  in  that  orbit. 

To  some  it  has  appeared  a  matter  of  surprise  that  the 
new  planet  was  not  sooner  discovered.  Le  Terrier's  sec- 
ond memoir,  which  assigned  the  probable  place  of  the 
disturbing  body,  was  presented  to  the  Academy  on  the 
first  of  June,  1846;  and  his  third  memoir  (containing 
every  thing  which  Dr.  Galle  had  in  his  possession  at  the 
time  of  his  discovery)  was  presented  August  31st;  yet 
Galle's  discovery  was  not  made  till  September  23d. 
"What  were  the  astronomers  of  Paris  doing  meanwhile  ? 
Why  did  they  not  immediately  point  their  telescopes  to 
the  heavens?  "Why  did  they  neglect  the  opportunity  of 
securing  to  France  the  glory  of  both  the  theoretical  and 
practical  discovery,  and  leave  to  a  German  astronomer 
the  verification  of  the  sublimest  theory  of  modern 
science  ?  The  answer  is  plain.  The  astronomers  of  Paris 
did  not  expect  to  find  a  planet  within  one  degree  of  the  place 
computed  by  Le  Verrier.  Le  Verrier  himself  did  not  ex- 


THE  PLANET  NEPTUNE.  51 

pect  it.  He  assigned  the  most  probable  place  of  his  planet 
in  longitude  325°.  He  expressed  the  opinion  that  its 
longitude  would  not  be  less  than  321°,  nor  more  than  335°. 
But  he  adds,  "If  the  planet  should  not  be  discovered 
within  these  limits,  then  we  must  extend  our  search  beyond 
them}'1  If  he  was  sure  of  being  able  to  find  his  planet 
without  a  long-continued  and  laborious  search,  why  did 
he  not  borrow  a  telescope,  and  at  once  verify  his  own 
predictions  ? 

Nor  had  the  astronomers  of  the  rest  of  Europe  much 
higher  faith  than  those  of  Paris.  Professor  Encke,  in 
announcing  the  discovery,  characterizes  it  as  "far  ex- 
ceeding any  expectations  which  could  have  been  previously 
entertained"  That  Professors  Airy  and  Challis,  although 
they  were  pretty  well  satisfied  of  the  existence  of  a  planet 
yet  undiscovered,  regarded  its  exact  place  in  the  heav- 
ens as  extremely  uncertain,  is  plain  from  their  compre- 
hensive plan  of  observation,  viz.,  to  sweep  three  times 
over  a  belt  of  the  heavens,  thirty  degrees  in  length,  and 
ten  degrees  in  breadth,  a  plan  which  Professor  Challis 
states  it  would  have  been  impossible  for  him  to  complete 
within  the  year  1846. 

Do  we  then  charge  Encke  and  Airy  with  a  want  of 
sagacity?  By  no  means.  On  the  contrary,  we  main- 
tain that  they  had  no  reason  to  expect  to  find  the  planet 
within  one  degree  of  the  computed  place.  Le  Vender's  own 
statement  of  the  limits  within  which  the  planet  should 
be  sought  for,  is  sufficient  proof  of  this.  "  L'incertitude 
des  donnees  pourrait  produire  une  incertitude  de  plus 


52  HISTORY  OF  ASTRONOMY. 

de  18  d^gres  dans  le  lieu  de  1'astre,  a  1'une  des  epoques 
ou  1'on  pouvait  le  mieux  repondre  de  sa  position.  The 
uncertainty  of  the  data  caused  an  uncertainty  of  more 
than  eighteen  degrees  in  the  position  of  the  planet,  even  at  the 
time  when  its  situation  was  lest  determined"  Professor 
Challis,  therefore,  proceeded  like  a  sagacious  as  well  as 
brave  general.  He  contemplated  a  long  siege — yet  his 
plan  rendered  ultimate  success  almost  certain.  Dr.  Galle 
took  the  citadel  by  storm — yet  he  had  no  reason  to  ex- 
pect so  easy  a  conquest.  His  success  must  have  as- 
tonished himself  as  much  as  it  did  the  world. 

Let  us  then  be  candid,  and  claim  for  astronomy  no 
more  than  is  reasonably  due.  When  in  1846  Le  Terrier 
announced  the  existence  of  a  planet  hitherto  unseen, 
when  he  assigned  its  exact  position  in  the  heavens,  and 
declared  that  it  shone  like  a  star  of  the  eighth  magnitude, 
and  with  a  perceptible  disc,  not  an  astronomer  of  France, 
and  scarce  an  astronomer  in  Europe,  had  sufficient  faith, 
in  the  prediction  to  prompt  him  to  point  his  telescope 
to  the  heavens.  But  when  it  was  announced  that  the 
planet  had  been  seen  at  Berlin  ;  that  it  was  found  within 
one  degree  of  the  computed  place  ;  that  it  was  indeed  a 
star  of  the  eighth  magnitude,  and  had  a  sensible  disc, 
then  the  enthusiasm  not  merely  of  the  public  generally, 
but  of  astronomers  also,  was  even  more  wonderful  than 
their  former  apathy.  The  sagacity  of  Le  Yerrier  was 
felt  to  be  almost  superhuman.  Language  could  hardly 
be  found  strong  enough  to  express  the  general  admira- 
tion. The  praise  then  lavished  upon  ,Le  Verrier  was 


THE  PLANET  NEPTUNE.  53 

somewhat  extravagant.  The  singularly  close  agreement 
between  the  observed  and  computed  places  of  the  planet 
was  accidental.  So  exact  a  coincidence  could  not  have 
been  reasonably  anticipated.  If  the  planet  had  been 
found  even  ten  degrees  from  what  Le  Yerrier  assigned 
as  its  most  probable  place,  this  discrepancy  would  have 
surprised  no  astronomer.  The  discovery  would  still 
have  been  one  of  the  most  remarkable  events  in  the 
history  of  astronomy,  and  Le  Yerrier  would  have  merited 
all  the  honors  which  have  since  been  conferred  upon 
him.  , 


SECTION    II. 

THE  ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER, 

SEVENTY-FIVE  years  since,  the  only  planets  known  to 
men  of  science  were  the  same  which  were  known  to 
the  Chaldean  shepherds  thousands  of  years  ago.  Between 
the  orbit  of  Mars  and  that  of  Jupiter,  there  occurs  an 
interval  of  no  less  than  350  millions  of  miles,  in  which 
no  planet  was  known  to  exist  before  the  commencement 
of  the  present  century.  Nearly  three  centuries  ago, 
Kepler  had  pointed  out  something  like  a  regular  pro- 
gression in  the  distances  of  the  planets  as  far  as  Mars, 
which  was  broken  in  tne  case  of  Jupiter.  Having  de- 
spaired of  reconciling  the  actual  state  of  the  planetary 
system  with  any  theory  he  could  form  respecting  it,  he 
hazarded  the  conjecture  that  a  planet  really  existed  be- 
tween the  orbits  of  Mars  and  Jupiter,  and  that  its  small- 
ness  alone  prevented  it  from  being  visible  to  astronom- 
ers. The  remarkable  passage  containing  this  conjecture 
is  found  in  his  Prodromus,  and  is  as  follows :  "  When  this 
plan,  therefore,  failed,  I  tried  to  reach  my  aim  in  another 
way,  of,  I  must  confess,  singular  boldness.  Between 
Jupiter  and  Mars  I  interposed  a  new  planet,  and  another 
also  between  Yenus  and  Mercury,  both  which  it  is  pos- 
sible are  not  visible  on  account  of  their  minuteness,  and 


ZONE   OF  PLANETS  BETWEEN  MARS  AND  JUPITER.     55 

I  assigned  to  them  their  respective  periods.  In  this  way 
I  thought  that  I  might  in  some  degree  equalize  their 
ratios,  which  ratios  regularly  diminished  toward  the  sun, 
and  enlarged  toward  the  fixed  stars." 

But  Kepler  himself  soon  rejected  this  idea  as  improb- 
able, and  it  does  not  appear  to  have  received  any  favor 
from  the  astronomers  of  that  time. 

An  astronomer  of  Florence,  by  the  name  of  Sizzi, 
maintained,  that  as  there  were  only  seven  apertures  in 
the  head — two  eyes,  two  ears,  two  nostrils,  and  one 
mouth — and  as  there  were  only  seven  metals  and  seven 
days  in  the  week,  so  there  could  be  only  seven  planets. 
These  seven  planets,  according  to  the  ancient  system  of 
astronomy,  were  Saturn,  Jupiter,  Mars,  the  Sun,  Venus, 
Mercury,  and  the  Moon. 

In  1772,  Bode  published  a  treatise  on  Astronomy,  in 
which  he  first  announced  the  singular  relation  between 
the  mean  distances  of  the  planets  from  the  sun,  which 
has  since  been  distinguished  by  his  name.  This  famous 
law  may  be  thus  stated.  If  we  set  down  the  number  four 
several  times  in  a  row,  and  to  the  second  4  add  3,  to 
the  third  4  add  twice  3  or  6,  to  the  next  4  add  twice  6 
or  12,  and  so  on,  as  in  the  following  table,  the  resulting 
numbers  will  represent  nearly  the  relative  distances  of  the 
planets  from  the  sun  : 


4 

4 

4 

4 

4 

4 

3 

6 

12 

24 

48 

96 

7 

10 

16 

28 

52 

100 

56  HISTORY  OF  ASTRONOMY. 

If  the  distance  of  the  Earth  from  the  Sun  be  called 
10,  then  4  will  represent  nearly  the  distance  of  Mercury ; 
7  that  of  Yenus  j  16  that  of  Mars ;  52  that  of  Jupiter; 
and  100  that  of  Saturn.  This  law  exhibited  in  a  striking 
light  the  abrupt  leap  from  Mars  to  Jupiter,  and  sug- 
gested the  probability  of  a  planet  revolving  in  the  inter- 
mediate region.  This  conjecture  was  rendered  still  more 
plausible  by  the  discovery,  in  1781,  of  the  planet  Uranus, 
whose  distance  from  the  sun  was  found  to  conform 
nearly  with  the  law  of  Bode.  In  Germany,  especially, 
a  strong  impression  had  been  produced  that  a  planet 
really  existed  between  Mars  and  Jupiter,  and  the  Baron 
de  Zach  went  so  far  as  to  calculate,  in  1784-5,  the  orbit 
of  the  ideal  planet,  the  elements  of  which  he  published 
in  the  Berlin  Almanac  for  1789.  In  1800,  six  astron- 
omers, of  whom  the  Baron  was  one,  assembled  at  Lilien- 
thal,  and  formed  an  association  of  twenty -four  observers, 
having  for  its  object  to  effect  the  discovery  of  the  unseen 
body.  For  this  purpose  the  zodiac  was  divided  into 
twenty-four  zones,  one  of  which  was  to  be  explored  by 
each  astronomer ;  and  the  conduct  of  the  whole  opera- 
tion was  placed  under  the  superintendence  of  Schroter. 
Soon  after  the  formation  of  this  society,  the  planet  was 
discovered,  but  not  by  any  of  those  astronomers  who 
were  engaged  expressly  in  searching  for  it.  Piazzi,  the 
celebrated  Italian  astronomer,  while  engaged  in  construct- 
ing his  great  catalogue  of  stars,  was  induced  carefully  to 
examine,  several  nights  in  succession,  a  part  of  the  con- 
stellation Taurus,  in  which  "Wollaston,  by  mistake,  had 


ZOXE   OF   PLANETS  BETWEEN  MARS  AND  JUPITER.     57 

assigned  the  position  of  a  star  which  did  not  really  exist. 
On  the  1st  of  January,  1801,  Piazzi  observed  a  small 
star,  which  on  the  following  evening  appeared  to  have 
changed  its  place.  On  the  3d  he  repeated  his  observa- 
tions, and  he  now  felt  assured  that  the  star  had  a  retro- 
grade motion  in  the  zodiac.  On  the  24th  of  January 
he  transmitted  an  account  of  his  discovery  to  Oriani  and 
Bode,  communicating  the  position  of  the  star  on  the  3d 
and  23d  of  that  month.  He  continued  to  observe  the 
star  until  the  llth  of  February,  when,  he  was  seized 
with  a  dangerous  illness,  which  completely  interrupted 
his  labors.  His  letters  to  Oriani  and  Bode  did  not  reach 
those  astronomers  until  the  latter  end  of  March,  at  which 
time  the  planet  had  approached  too  near  the  sun 'to 
admit  of  further  observations,  and  it  was  necessary  for 
this  purpose  to  wait  until  the  month  of  September,  when 
the  planet  would  have  extricated  itself  from  the  solar 
rays.  Its  re-discovery,  after  the  lapse  of  so  considerable 
a  period,  subsequent  to  the  most  recent  observation, 
could  not  be  accomplished  without  a  pretty  accurate 
knowledge  of  the  orbit  in  which  it  was  moving;  but 
the  data  communicated  by  Piazzi  were  insufficient  for 
this  purpose.  After  some  delay  he  communicated  to 
astronomers  all  the  observations  made  by  himself  down 
to  the  end  of  February.  Professor  Gauss  found  that 
they  might  all  be  satisfied  within  a  few  seconds  by  an 
elliptic  orbit,  of  which  he  calculated  the  elements;  and 
with  the  view  of  aiding  astronomers  in  searching  for  the 
planet,  he  computed  an  ephemeris  of  its  motion  for 

3* 


58  HISTORY    OF  ASTRONOMY. 

several  months.  The  planet  was  finally  discovered  by 
De  Zach  on  the  31st  of  December,  and  by  Olbers  on  the 
following  evening.  Piazzi  conferred  on  it  the  name  of 
Ceres,  in  allusion  to  the  titular  goddess  of  Sicily,  the 
island  in  which  it  was  discovered;  and  the  sickle  has 
been  appropriately  chosen  for  its  symbol  of  designation. 
The  mean  distance  of  Ceres,  as  determined  by  the  cal- 
culations of  Gauss,  was  2*767.  The  distance  assigned  by 
Bode's  law  was  2*8.  In  this  respect,  therefore,  the  newly- 
discovered  planet  harmonized  with  the  other  bodies  of 
the  system  to  which  it  belonged.  The  new  planet  was, 
however,  excessively  minute ;  its  diameter,  according  to 
Herschel's  measurements,  amounting  to  only  161  miles. 
Its  inclination  to  the  ecliptic  exceeded  ten  degrees,  and 
consequently  it  deviated  from  that  plane  more  than  either 
of  the  older  planets. 

The  discovery  of  Piazzi  was  soon  followed  by  another 
of  a  similar  nature.  Dr.  Olbers,  while  engaged  in 
searching  for  Ceres,  had  studied  with  minute  attention 
•  the  various  configurations  of  all  the  small  stars  lying 
near  her  path.  On  the  28th  of  March,  1802,  after  ob- 
serving the  planet,  he  swept  over  the  north  wing  of 
Virgo  with  an  instrument  termed  a  "  Comet  Seeker," 
and  was  astonished  to  find  a  star  of  the  seventh  magni- 
tude, forming  an  equilateral  triangle  with  two  other  small 
stars,  whose  positions  were  given  in  Bode's  catalogue, 
where  he  was  certain  no  star  was  visible  in  January  and 
February  preceding.  In  the  course  of  less  than  three 
hours  he  found  the  right,  ascension  had  diminished,  and 


ZONE   OF  PLANETS  BETWEEN  MARS  AND   JUPITER.     59 

the  north  declination  increased.  On  the  following  even- 
ing, as  soon  as  the  twilight  permitted,  he  looked  again 
for  his  star ;  it  no  longer  formed  an  equilateral  triangle 
with  the  stars  above  mentioned,  but  had  moved  con- 
siderably in  the  direction  indicated  by  the  preceding 
night's  observations.  On  the  30th,  after  again  observing 
the  planet,  Dr.  Olbers  wrote  to  Bode  at  Berlin,  and  to 
Baron  De  Zach,  giving  an .  account  of  his  discovery. 
"  What  a  singular  accident,"  he  exclaims,  uwas  it  by 
which  I  found  this  stranger  nearly  in  the  same  place 
where  I  had  observed  Ceres  on  the  1st  of  January !' 
The  elements  of  the  orbit  were  quickly  determined  by 
Professor  Gauss,  who  found  the  most  remarkable  pe- 
culiarity consisted  in  the  great  inclination  of  its  plane  to 
the  ecliptic,  which  amounted  to  34°  35'.  The  orbit  was 
found  to  be  an  ellipse  of  not  much  greater  eccentricity 
than  that  of  Mercury,  with  a  mean  distance  nearly  the 
same  as  that  of  Ceres.  Dr.  Olbers  suggested  Pallas  as  the 
name  for  this  new  member  of  our  system. 

A  comparison  of  the  relative  magnitudes  of  the  planet- 
ary orbits  had  suggested  the  existence  of  an  unknown 
planet,  revolving  between  the  orbits  of  Mars  and  Jupiter. 
Instead  of  one  planet,  however,  tw6  had  been  discovered. 
Olbers  remarked  that  the  orbits  of  these  two  bodies  ap- 
proached very  near  each  other  at  the  descending  node  of 
Pallas,  and  he  conjectured  that  they  might  possibly  be 
the  fragments  of  a  larger  planet  which  had  once  revolved 
in  the  same  region,  and  had  been  shivered  in  pieces  by 
some  tremendous  catastrophe ;  and  he  intimated  that 


60  HISTORY  OF  ASTRONOMY. 

fhere  might  be  many  more  similar  fragments  which,  had 
not  yet  been  discovered.  He  also  inferred,  that  though 
the  orbits  of  all  these  fragments  might  be  differently  in- 
clined to  the  ecliptic,  yet,  as  they  all  had  a  common 
origin,  their  orbits  would  have  two  common  points  of  in- 
tersection, situated  in  opposite  regions  of  the  heavens, 
through  which  every  fragment  would  necessarily  pass  in 
the  course  of  each  revolution.  He  proposed,  therefore,  to 
search  carefully,  every  month,  the  north-western  part  of 
the  constellation  Virgo,  and  the  western  part  of  the  con- 
stellation of  the  Whale,  being  the  two  opposite  regions  in 
which  the  orbits  of  Ceres  and  Pallas  were  found  to  inter- 
sect each  other.  Meanwhile  the  discovery  of  a  third 
planet  tended  to  confirm  the  truth  of  his  hypothesis,  and 
to  encourage  him  in  his  arduous  undertaking. 

Professor  Harding,  of  Lilienthal,  undertook  to  con- 
struct a  series  of  charts  upon  which  should  be  represented 
the  positions  of  all  the  small  stars  lying  near  the  paths  of 
Ceres  and  Pallas,  with  a  view  to  assist  the  identification 
of  these  minute  bodies.  On  the  1st  of  September,  1804, 
while  engaged  in  exploring  the  heavens  for  this  purpose, 
he  perceived  a  small  star  in  the  constellation  Pisces, 
very  near  to  that  part  of  the  constellation  of  the  "Whale 
through  which  Olbers  had  asserted  that  the  fragments  of 
the  shattered  planet  would  be  sure  to  pass.  On  the  even- 
ing of  the  4th  he  re-examined  the  neighborhood,  and 
found  that  the  star  had  changed  its  place.  On  the  5th 
and  6th,  he  observed  it  more  accurately,  and  finding  that 
the  positions  deduced  from  his  observations  confirmed  the 


ZONE   OF  PLANETS  BETWEEN  MARS  AND    JUPITER.     61 

motion  indicated  by  the  estimates  on  September  1st  and 
4th,  he  announced  the  discovery  to  Dr.  Gibers,  at 
Bremen,  on  the  7th,  who  saw  it  the  same  evening.  Pro 
fessor  Harding  named  his  planet  Juno.  The  elements  of 
its  orbit  were  calculated  by  Gauss,  who  found  its  mean 
distance  from  the  sun  to  coincide  nearly  with  the  mean 
distances  of  Ceres  and  Pallas.  The  eccentricity  surpass- 
ed that  of  any  other  member  of  the  planetary  system. 
Like  Ceres  and  Pallas,  it  is  remarkable  for  its  extreme 
smallness.  Herschel  was  unable  to  pronounce  with  cer- 
tainty that  its  diameter  exhibited .  any  sensible  magni- 
tude. 

Stimulated  by  the  discovery  of  Juno,  Gibers  continued 
with  unremitting  assiduity  to  explore  the  two  opposite  re- 
gions of  the  heavens  through  which  he  conceived  the 
fragments  of  the  shattered  planet  must  pass.  At  length, 
after  he  had  been  engaged  nearly  three  years  in  this  la- 
borious pursuit,  his  perseverance  was  crowned  with  suc- 
cess. Gn  the  evening  of  the  29th  of  March,  1807,  while 
occupied  in  sweeping  over  the  north  wing  of  Virgo,  he 
discovered  an  object  shining  like  a  star  of  the  sixth  or 
seventh  magnitude,  which  he  concluded  at  once  to  be  a 
planet,  inasmuch  as  the  previous  examination  of  the 
vicinity  had  indicated  no  star  in  the  position  of  the 
stranger.  Gn  the  same  evening  he  satisfied  himself  that 
it  was  really  in  motion,  and  continuing  his  observations 
until  the  2d  of  April,  he  obtained  sufficient  evidence  to 
justify  the  public  announcement  of  his  discovery  of 
another  new  planet.  Accordingly,  on  the  following  day, 


62  HISTOEY  OF  ASTRONOMY. 

he  wrote  to  Professor  Bode  of  Berlin,  and  to  Baron  de 
Zach  of  G  otha,  and  particularly  mentioned  that  his  sec- 
ond discovery  was  not  the  result  of  accident,  but  of  a 
systematic  search  for  a  body  of  this  nature.  The  ele- 
ments of  the  orbit  were  determined  by  Gauss,  who  ex- 
ecuted the  calculations  required  for  this  purpose  within 
ten  hours  after  he  obtained  possession  of  the  observations. 
The  planet  was  found  to  revolve  in  the  same  region  with 
Ceres,  Pallas,  and  Juno,  its  mean  distance  from  the  sun 
being  somewhat  less  than  that  of  either  of  those  bodies. 
At  the  request  of  Dr.  Olbers,  Gauss  consented  to  name 
the  planet,  and  decided  upon  Yesta,  the  symbol  of  desig- 
nation being  the  altar  on  which  burned  the  sacred  fire  in 
honor  of  the  goddess.  This  planet  is  even  smaller  than 
either  of  the  three  others  previously  discovered,  but  it  is 
remarkable  for  the  brilliancy  of  its  light.  Near  her  op- 
position to  the  sun,  a  person  with  good  sight  may  often 
distinguish  her  without  a  telescope. 

Dr.  Olbers  continued  his  systematic  examinations  of  the 
small  stars  in  Yirgo  and  Cetus,  between  the  years  1808 
and  1816,  and  was  so  closely  on  the  watch  for  any  mov- 
ing body,  that  he  considered  it  very  improbable  a  planet 
could  have  passed  through  either  of  these  regions  in  the 
interval,  without  being  detected.  No  further  discovery 
being  made,  the  plan  was  relinquished  in  1816. 

In  1825,  a  fresh  impulse  was  given  to  researches  of 
this  nature,  by  the  resolution  of  the  Berlin  Academy  of 
Sciences  to  procure  the  construction  of  a  series  of  charts 
representing  the  positions  of  all  the  stars,  down  to  the 


ZONE  OF  PLANETS  BETWEEN  MAES  AND  JUPITER.     63 

ninth  magnitude,  in  a  zone  of  the  heavens  extending  fif- 
teen degrees  on  each  side  of  the  equator.  Only  about 
two  thirds  of  the  charts  contemplated  in  this  great  under- 
taking have  yet  been  executed. 

About  the  year  1830,  M.  Hencke,  an  amateur  astrono- 
mer of  Driessen,  in  Germany,  commenced  a  careful  sur- 
vey of  the  zone  of  the  heavens  comprised  within  the 
charts  published  by  the  Academy  of  Berlin.  He  ex- 
tended those  maps  by  the  insertion  of  smaller  stars,  and 
made  himself  well  acquainted  with  their  various  configu- 
rations. After  fifteen  years  his  perseverance  met  with  its 
due  reward.  On  the  8th  of  December,  1845,  while  en- 
gaged in  comparing  the  map  of  the  fourth  hour  of  right 
ascension  with  the  heavens,  he  noticed  what  appeared  to 
be  a  star  of  the  ninth  magnitude,  between  two  others  of 
the  same  brightness  in  Taurus,  which  had  not  been 
noted  in  his  previous  examinations.  Without  waiting 
for  any  further  observations,  M.  Hencke  wrote  to  Pro- 
fessors Encke  and  Schumacher,  stating  his  reasons  for 
supposing  that  he  had  detected  a  new  planet.  On  the 
14th  of  December  the  Berlin  astronomers  found  the 
stranger  in  a  position  where  no  star  was  marked  on  the 
corresponding  chart  of  the  Academy,  and  the  motion  was 
easily  perceived  the  same  evening.  On  this  occasion  the 
elements  of  the  orbit  were  rapidly  determined,  not  by 
Gauss  individually,  as  on  previous  occasions  of  a  similar 
kind,  but  by  a  host  of  young  astronomers  throughout 
Europe,  who  had  become  familiar  with  the  methods  of 
that  illustrious  master.  The  results  of  their  calculations 


64  HISTOKY  OF  ASTRONOMY. 

showed  the  body  to  be  one  of  the  family  of  asteroids.  M. 
Hencke  requested  Professor  Encke  to  name  his  new 
planet,  and  the  Professor  conferred  on  it  the  appellation 
of  Astraea. 

Encouraged  by  his  success,  M.  Hencke  continued  his 
search  for  planetary  bodies,  extending  and  verifying  the 
Berlin  Academical  charts,  and  by  frequent  comparison 
with  the  heavens  acquired  an  extensive  knowledge  of  the 
configurations  of  the  smaller  stars  in  certain  regions 
about  the  equator  and  ecliptic.  On  the  1st  of  July,  1847, 
while  engaged  in  examining  the  seventeenth  hour  of 
right  ascension,  he  perceived  a  small  star,  of  about  the 
ninth  magnitude,  which  was  not  marked  on  the  cor- 
responding map  of  the  Academy.  On  the  3d,  he  repeat- 
ed his  observation,  and  found  that,  during  the  intermedi- 
ate period,  its  right  ascension  had  sensibly  diminished, 
leaving  no  doubt  of  its  planetary  nature.  Information  of 
the  discovery  was  circulated  by  M.  Hencke  on  the  follow- 
ing day,  and  the  planet  was  soon  recognized  at  the  prin- 
cipal observatories  of  Europe.  The  illustrious  mathe- 
matician, Professor  Gauss,  was  deputed  by  the  discoverer 
to  select  a  name  for  the  stranger,  and  it  received  the  name 
of  Hebe,  with  a  cup  for  the  symbol,  emblematic  of  the 
office  of  the  goddess  in  mythology.  The  orbit  is  very 
eccentric,  and  inclined  more  than  14  degrees  to  the  plane 
of  the  ecliptic. 

The  next  two  members  of  this  remarkable  group  in 
order  of  discovery  were  found  by  Mr.  Hind,  at  the  ob- 
servatory erected  by  Mr.  Bishop,  in  the  grounds  of  his 


ZONE   OF  PLANETS  BETWEEN  MAES  AND  JUPITER.     65 

private  residence  in  the  Kegent's  Park,  London.  So 
early  as  April,  1845,  a  search  for  planetary  bodies  was 
commenced,  but  in  consequence  of  other  classes  of  ob- 
servation, no  systematic  plan  of  examination  of  the 
heavens  was  attempted.  In  November,  1846,  a  rigorous 
search  was  undertaken,  the  Berlin  Academical  charts  be- 
ing employed  as  far  as  they  extended;  while  ecliptic 
charts,  including  stars  to  the  tenth  magnitude,  were 
formed  for  other  parts  of  the  heavens,  where  the  ecliptic 
passes  beyond  the  limits  of  the  Berlin  maps.  On  the 
13th  of  August,  1847,  after  nine  months'  close  observa- 
tion on  the  above  system,  an  object  resembling  a  star  of 
the  eighth  magnitude  was  discovered,  which  was  not 
marked  on  the  corresponding  Berlin  map.  Its  planetary 
nature  being  immediately  suspected,  it  was  attentively 
observed,  and  in  less  than  half  an  hour  the  motion  in 
right  ascension  was  detected.  In  the  course  of  an  hour 
the  planet  had  retrograded  two  seconds  of  time,  a  suffi- 
cient change  of  place  to  be  indubitable.  An  announce- 
ment of  the  discovery  was  made  to  astronomers  generally 
on  the  following  morning,  and  observations  were  soon 
obtained  at  most  of  the  European  observatories.  At  the 
suggestion  of  Mr.  Bishop  the  planet  was  named  Iris.  The 
symbol  is  due  to  Professor  Schumacher,  and  is  composed 
of  a  semicircle  representing  the  rainbow,  with  an  interior 
star,  and  a  base  line  for  the  horizon.  Several  observers 
have  remarked  decided  variations  in  the  light  of  this 
planet,  which  are  not  accounted  for  by  change  of  distance 
from  the  earth  and  sun,  and  which  there  is  strong  reason 


66  HISTORY  OF  ASTKONOMY. 

to  suppose  are  in  a  great  measure  independent  of  atmos- 
pheric conditions. 

Continuing  the  plan  of  observation  already  described, 
Mr.  Hind  noticed,  on  the  18th  of  October,  1847,  in  the 
constellation  Orion,  a  star  of  the  eighth  or  ninth  magni- 
tude, which  had  not  been  previously  visible  in  the  posi- 
tion it  then  occupied.  Micrometrical  measures  of  its 
position,  made  after  the  lapse  of  about  four  hours  from 
the  time  when  he  first  observed  it,  established  the  exist- 
ence of  a  proper  motion,  and  it  was  immediately  an- 
nounced to  astronomers  as  the  eighth  member  of  the 
group  of  small  planets.  At  the  suggestion  of  Sir  John 
Herschel  the  new  planet  received  the  name  Flora,  and  a 
flower,  the  "  rose  of  England,"  was  chosen  as  the  sym- 
bol. Its  period  of  revolution  is  shorter  than  that  of  any 
other  of  the  asteroids,  being  only  about  1193  days. 
Flora,  therefore,  comes  after  Mars  in  order  of  mean  dis- 
tance from  the  sun,  and  approaches  nearer  to  the  earth 
than  the  rest  of  the  group  to  which  she  belongs.  The 
planet  is  somewhat  ruddy,  but  without  any  hazy  appear- 
ance, such  as  might  be  supposed  to  arise  from  an  exten- 
sive atmosphere. 

In  the  year  1848  another  member  of  this  interesting 
group  was  brought  to  light  by  Mr.  Graham,  at  the  private 
observatory  of  Markree  Castle,  Ireland,  under  the  direc- 
tion of  Mr.  Cooper.  Having  formed  a  chart  of  the  stars 
near  the  equator,  in  the  14th  hour  of  right  ascension,  on 
a  more  extended  scale  than  that  of  the  Berlin  charts,  he 
remarked,  on  the  25th  of  April,  a  star  of  the  tenth  mag- 


ZONE   OF   PLANETS  BETWEEN  MAES  AND  JUPITEE.     67 

nitude  in  a  position  where  none  had  been  visible  before, 
and  noted  it  down  for  re-examination.  On  the  following 
evening  this  object  was  found  to  have  retrograded  one 
minute,  thus  leaving  no  doubt  of  its  planetary  nature. 
On  the  27th  the  discovery  was  announced  to  several  as- 
tronomers in  England  and  on  the  Continent,  and  soon 
became  generally  known  through  the  circulars  issued  by 
Professor  Schumacher.  The  name  selected  for  this  planet 
is  Metis,  with  an  eye  and  star  for  a  symbol.  This  planet 
is  remarkable  for  the  near  coincidence  of  its  mean  motion 
with  that  of  Iris,  the  duTerence  of  their  periodic  times, 
according  to  the  most  recent  calculations,  amounting  to 
less  than  one  day. 

On  the  12th  of  April,  1849,  Dr.  Annibal  de  Gasparis, 
assistant  astronomer  at  the  royal  observatory  at  Naples, 
while  comparing  the  Berlin  chart  for  the  twelfth  hour 
of  right  ascension  with*  the  heavens,  perceived  a  star  of 
between  the  ninth  and  tenth  magnitudes,  in  a  position 
which  he  had  found  vacant  at  previous  examinations  of 
this  region.  Unfavorable  weather  interrupted  his  ob- 
servations for  that  evening,  but  on  the  14th  he  ascer- 
tained that  it  had  sensibly  changed  its  place,  and  was 
therefore  a  new  planet.  Professor  Capocci,  director  of 
the  Neapolitan  observatory,  named  the  planet  Hygeia. 
The  mean  distance  of  this  planet  from  the  sun  is,  with 
perhaps  a  single  exception,  greater  than  that  of  any  other 
known  member  of  this  group,  corresponding  to  a  revolu- 
tion in  2041  days. 

On  the  occasion  of  the  discovery  of  Hygeia,  Sir  John 


68  HISTOEY  OF  ASTRONOMY. 

Herschel  had  suggested  that  Parthenope  would  be  a  very 
appropriate  name  to  commemorate  the  site  of  the  dis- 
covery ;  that  nymph  having  given  her  name  to  the  city 
now  called  Naples.  Signor  de  Gasparis  states  that  he 
used  his  utmost  exertions  to  realize  for  Sir  John  Herschel 
a  Parthenope  in  the  heavens,  and  his  endeavors  were 
crowned  with  success  on  the  llth  of  May,  1850.  This 
new  planet  appeared  like  a  star  of  the  ninth  magnitude. 

On  the  evening  of  September  13,  1850,  Mr.  Hind 
noticed  a  star  of  the  eighth  magnitude  in  the  constel- 
lation Pegasus,  near  another  small  one  frequently  ex- 
amined on  previous  occasions,  without  any  mention 
being  made  of  its  bright  neighbor.  Its  peculiar  bluish 
light  satisfied  him  at  once  as  to  its  planetary  nature,  and 
the  micrometer  was  introduced  to  ascertain  the  difference 
of  right  ascension  between  the  two  objects,  and  to  ob- 
tain conclusive  proof  of  the  discovery  of  a  new  planet. 
In  less  than  an  hour  the  brighter  star  had  moved  west- 
ward about  two  seconds  of  time,  so  that  no  doubt  could 
be  entertained  in  respect  to  its  nature  and  position  in 
the  solar  system.  Mr.  Hind  selected  for  this  planet  the 
name  Victoria,  with  a  star  and  laurel -branch  for  its  sym- 
bol. In  case,  however,  this  name  should  be  considered 
objectionable,  he  proposed  that  of  Clio,  which  name  has 
been  generally  preferred  by  American  astronomers. 

Eemarkable  changes  of  brilliancy  in  this  body  have 
been  noticed  at  the  Washington  observatory.  On  the 
night  of  November  4,  1850,  the  planet  appeared  of  the 
tenth  magnitude.  On  the  succeeding  night  it  had  dimin  - 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.      69 

ished  to  the  twelfth  magnitude,  while  the  star  of  com- 
parison exhibited  no  perceptible  change.  Differences  to 
a  greater  amount  were  observed  between  the  22d  and 
25th  of  February,  1851.  On  the  nights  of  the  1st  and 
2d  of  March,  1851,  it  appeared  as  a  star  of  the  twelfth 
magnitude,  and  was  observed  without  difficulty ;  the  star 
of  comparison  being  near,  and  of  about  the  same  magni- 
tude. On  the  night  of  the  3d,  Clio  could  barely  be  ob- 
served with  the  faintest  illumination,  while  the  same  star 
of  comparison  used  on  the  nights  of  the  1st  and  2d  ap- 
peared as  before.  On  the  night  of  the  4th  the  planet 
appeared  even  more  brilliant  than  it  did  on  the  nights 
of  the  1st  and  2d  instant.  These  changes  seem  to  sug- 
gest the  probability  that  the  light  is  reflected  with  un- 
equal intensity  from  different  sides  of  this  asteroid. 
Similar  differences  of  magnitude  in  the  other  asteroids 
have  been  noticed,  particularly  in  Astraea. 

The  discovery  of  Victoria  was  soon  followed  by  that 
of  another  asteroid  by  Dr.  Annibal  de  Gasparis,  at  the 
royal  observatory,  Naples.  In  this  case  a  star  map  was 
not  the  means  of  discovering  the  planet,  but  its  existence 
was  indicated  by  a  series  of  observations  in  zones  of  de- 
clination, which  had  been  undertaken  for  the  express 
purpose  of  finding  new  planets.  On  the  2d  of  Novem- 
ber, 1850,  Dr.  Gasparis  met  with  the  thirteenth  asteroid 
in  the  constellation  Cetus.  It  was  sensibly  fainter  than 
stars  of  the  ninth  magnitude.  M.  Le  Yerrier,  to  whom 
was  delegated  the  right  of  naming  this  planet,  proposed 
Egeria,  the  counselor  of  Numa  Pompilius.  The  orbit  is 


70  HISTORY  OF  ASTRONOMY. 

more  inclined  to  the  plane  of  the  ecliptic  than  that  of 
most  of  the  other  planets. 

The  next  member  of  the  group  of  small  planets  in  the 
order  of  discovery,  was  found  by  Mr.  Hind  in  the  con- 
stellation Scorpio,  on  the  19th  of  May,  1851,  and  four 
days  later  by  Dr.  Gasparis,  at  Naples.  It  appeared  like 
a  star  of  between  the  eighth  and  ninth  magnitudes,  with 
a  full  blue  light,  and  seemed  to  be  surrounded  by  a 
faint  nebulous  envelope  or  atmosphere,  which  could  not 
be  perceived  about  stars  of  equal  brightness.  The  nature 
of  this  object  was  satisfactorily  established  within  half 
an  hour  from  the  first  glimpse  of  it  on  the  19th  of  May ; 
repeated  examinations  of  the  vicinity  on  previous  oc- 
casions having  indicated  no  star  in  the  position  of  the 
stranger.  At  the  recommendation  of  Sir  John  Herschel 
the  new  planet  was  named  Irene,  in  allusion  to  the  peace 
prevailing  at  that  time  in  Europe ;  the  symbol  proposed 
being  a  dove  with  an  olive-branch  and  star  on  its  head. 

On  the  night  of  July  29,  1851,  another  small  planet 
was  discovered  by  Dr.  Gasparis,  at  Naples,  in  the  course 
of  his  zone  observations,  commenced  with  an  especial  view 
to  the  discovery  of  new  planets.  It  shone  as  a  fine  star 
of  the  ninth  magnitude ;  but,  owing  to  its  low  situation 
in  the  heavens,  was  not  so  generally  observed  during 
its  first  apparition  as  some  of  the  other  newly-discovered 
bodies.  Dr.  Gasparis  named  his  planet  Eunomia,  who 
in  classical  mythology  was  one  of  the  Seasons,  a  sister  of 
Irene. 

On  the  17th  of  March,  1852,  M.  de  Gasparis,  at  Naples, 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.     71 

discovered  another  small  planet  near  the  bright  star 
Kegulus.  It  appeared  like  a  small  star  of  the  tenth  or 
eleventh  magnitude,  and*  has  received  the  name  of 
Psyche.  Mr.  Hind,  of  London,  narrowly  missed  the 
honor  of  being  the  first  discoverer  of  this  body.  On 
the  29th  of  January  preceding,  he  entered  upon  his  chart 
a  star  of  the  eleventh  magnitude  in  the  place  where,  ac- 
cording to  subsequent  computations,  this  planet  ought  to 
have  been.  The  chart  was  immediately  sent  to  the  en- 
graver, and  not  returned  until  March  18;  but  on  the 
evening  of  that  day  he  discovered  that  the  above  star 
was  missing.  He  immediately  commenced  a  search  for 
the  planet,  and  actually  recorded  it  again  on  the  20th  as 
a  fixed  star,  but  moonlight  and  unfavorable  weather 
prevented  him  from  establishing  its  planetary  nature 
before  he  received  the  announcement  of  Dr.  Grasparis' 
discovery. 

On  the  17th  of  April,  1852,  another  planet  was  dis- 
covered near  Flora  by  Mr.  E.  Luther,  at  the  observatory 
at  Bilk,  near  Diisseldorf.  Professor  Argelander,  of  Bonn, 
proposed  for  this  planet  the  name  of  Thetis,  which  name 
was  accepted  by  the  discoverer,  and  has  been  adopted  by 
astronomers. 

On  the  25th  of  June,  1852,  Mr.  Hind,  at  London,  dis- 
covered another  planet,  having  the  appearance  of  a  star 
of  the  ninth  magnitude,  and  of  a  yellowish  light.  Mr. 
Airy,  the  astronomer  royal,  having  been  requested  by 
Mr.  Bishop  to  select  a  name  for  this  planet,  proposed  to 
call  it  Melpomene.  It  is  the  nearest  of  the  group  of 


72  HISTORY  OF  ASTRONOMY. 

asteroids,  except  Flora,  making  its  revolution  in  about 
1269  days. 

On  the  22d  of  August,  1852,  Mr.  Hind  discovered 
another  planet  not  far  from  the  ecliptic  in  the  constella- 
tion Aquarius.  It  appeared  like  a  star  of  the  ninth 
magnitude,  and  exhibited  the  same  yellowish  color  which 
was  remarked  about  Melpomene.  Mr.  Hind  having  been 
requested  by  Mr.  Bishop  to  find  a  name  for  this  planet, 
proposed  to  call  it  For  tun  a. . 

The  next  planet  was  independently  discovered  by  Pro- 
fessor de  Gasparis  on  September  19th,  and  by  M.  Cha- 
cornac,  assistant  to  M.  Yalz,  at  Marseilles,  on  the  20th  of 
the  same  month.  M.  Chacornac  was  occupied  in  com- 
pleting some  ecliptic  charts  of  the  stars  according  to  a 
plan  adopted  by  Professor  Yalz  in  1847,  and  on  the  night 
of  September  10,  he  remarked  a  star  of  the  ninth  mag- 
nitude in  a  position  where  none  had  been  seen  before. 
M.  Yalz  proposed  the  name  Massilia  for  this  object,  in 
which  Professor  Gasparis,  who  had  a  prior  claim  to  the 
discovery,  appears  to  have  concurred.  The  inclination 
of  its  orbit  to  the  ecliptic  is  less  than  that  of  any  other 
known  planet,  Uranus  not  excepted. 

On  the  15th  of  November,  1852,  another  planet  was 
discovered,  at  Paris,  by  M.  Hermann  Goldschmidt,  an 
historical  painter,  residing  in  that  city.  M.  Arago 
proposed  to  call  it  Lutetia.  It  resembled  a  star  of  the 
ainth  or  tenth  magnitude. 

On  the  night  following  the  last  discovery,  November 
L6th,  Mr.  Hind,  of  London,  detected  a  new  planet  with 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.     73 

the  assistance  of  one  of  the  ecliptical  star-maps  at  present 
in  course  of  publication  from  Mr.  Bishop's  observatory. 
It  was  not  much  over  the  tenth  magnitude,  which  is 
rather  beyond  the  limit  of  the  Berlin  charts.  Mr.  J.  C. 
Adams,  president  of  the  Astronomical  Society  of  Lon- 
don, being  requested  to  name  the  planet,  proposed  to  call 
it  Calliope. 

On  the  15th  of  December,  1852,  another  planet  was 
detected  by  Mr.  Hind.  It  had  a  pale,  bluish  light,  and 
resembled  a  star  of  the  tenth  or  eleventh  magnitude,  and 
being  not  very  far  from  perihelion,  is  probably  one  of 
the  faintest  members  of  the  group.  Mr.  Bishop,  at  the 
request  of  Mr.  Hind,  has  selected  for  this  planet  the  name 
Thalia. 

Thus,  within  a  period  of  nine  months,  were  discovered 
eight  small  planets  belonging  to  the  group  between  Mars 
and  Jupiter,  and  four  of  them  were  discovered  by  Mr. 
Hind  of  London,  a  fact  altogether  without  precedent  in 
the  history  of  astronomy — a  result  not  of  accident,  but 
of  a  systematic  and  persevering  survey  of  the  heavens. 

On  the  5th  of  April,  1853,  Professor  de  Gasparis  dis- 
covered in  the  constellation  Leo  a  very  minute  object, 
estimated  as  not  brighter  than  a  star  of  the  twelfth  mag- 
nitude, which  on  the  following  evening  he  recognized 
as  a  new  planet,  in  consequence  of  its  proper  motion. 
This  discovery  was  ascribed  to  the  circumstance,  that  on 
the  5th  of  April,  1851,  very  near  to  the  place  where  this 
planet  was  found,  he  had  observed  a  star  of  the  twelfth 

magnitude,  which  had  subsequently  vanished ;  for  which 

4 


74  HISTORY    OF  ASTRONOMY. 

i 

reason  he  was  led  to  examine  the  neighboring  stars  with 
unusual  care.  Professor  Secchi,  having  been  invited  by 
Professor  de  Gasparis  to  select  a  name  for  this  planet, 
proposed  the  name  of  Themis,  the  same  which  Professor 
de  Gasparis  had  originally  proposed  for  Massilia.  The 
mean  distance  of  Themis  from  the  sun  is  greater  than 
that  of  any  other  known  asteroid,  excepting  Hygeia 
and  Euphrosyne,  corresponding  to  a  period  of  2037 
days. 

On  the  night  after  the  preceding  discovery,  April  6th, 
M.  Chacornac,  at  Marseilles,  discovered  another  small 
planet.  It  appeared  of  a  bluish  tint,  and  of  the  size  of 
a  star  of  the  ninth  magnitude.  M.  Valz  proposed  to  call 
this  planet  Phocaea,  Marseilles  having  been  founded  by  a 
colony  from  Phocaea. 

On  the  5th  of  May,  1853,  Mr.  E.  Luther,  director  of 
the  observatory  at  Bilk,  near  Diisseldorf,  discovered  a 
new  planet  like  a  star  of  the  eleventh  magnitude.  This 
planet  was  christened  by  the  celebrated  Baron  von  Hum- 
boldt,  who  selected  for  it  the  name  of  Proserpina,  with 
the  symbol  of  a  pomegranate  and  a  star  in  its  center. 

On  the  8th  of  November,  1853,  Mr.  Hind  discovered 
another  planet  within  the  limits  of  his  ecliptical  chart  for 
the  third  hour  of  right  ascension.  It  was  as  bright  as 
stars  of  the  ninth  magnitude,  and  its  light  appeared  re- 
markably blue.  This  planet  has  received  the  name  of 
Euterpe. 

On  the  1st  of  March,  1854,  Mr.  E.  Luther,  director 
of  the  observatory  at  Bilk,  near  Diisseldorf,  discovered 


ZONE   OF  PLANETS  BETWEEN  MARS  AND  JUPITER.      75 

another  planet.  It  appeared  like  a  star  of  the  tenth 
magnitude,  and  has  received  from  Professor  Encke  the 
name  Bellona ;  the  symbol  proposed  being  a  whip  and 
a  lance. 

On  the  same  night  as  the  preceding,  but  about  two 
hours  later,  Mr.  Albert  Marth,  at  the  Regent's  Park  ob- 
servatory in  London,  discovered  another  planet  near 
Spica  Virginis.  It  appeared  like  a  star  of  the  tenth  or 
eleventh  magnitude,  and  Mr.  Bishop  has  proposed  for  it 
the  name  Amphitrite.  On  the  2d  of  March  the  same 
object  was  independently  discovered  at  the  Radcliffe  ob- 
servatory, Oxford,  England,  by  Mr.  Pogson,  who  for 
several  years  has  devoted  his  leisure  hours,  after  the 
regular  duties  of  his  office  are  completed,  to  the  formation 
of  charts  of  small  stars,  with  the  view  to  the  detec- 
tion of  new  planets  or  variable  stars.  A  third  independ- 
ent discovery  was  made  on  the  3d  of  March  by  M. 
Chacornac,  assistant  observer  at  the  observatory  of  Paris. 
The  same  impression  of  the  Times  contained  two  inde- 
pendent communications  from  Mr.  Hind  of  London,  and 
Mr.  Johnson  of  Oxford,  each  containing  the  announce- 
ment of  this  discovery.  Also,  on  the  4th  of  February, 
at  Marseilles,  M.  Chacornac  noted  a  star  of  the  tenth 
magnitude,  which  is  now  wanting  in  that  place,  and 
which  is  shown  to  have  been  the  body  first  recognized 
as  a  planet  by  Mr.  Marth. 

On  the  22d  of  July,  1854,  the  thirtieth  asteroid  was 
discovered  by  Mr.  Hind  at  Mr.  Bishop's  observatory  in 
Regent's  Park,  London.  It  appeared  like  a  star  between 


76  HISTORY  OF  ASTRONOMY. 

the  ninth,  and  tenth  magnitudes.  Professor  de  Morgan, 
who  was  requested  by  Mr.  Bishop  to  find  a  name  for  this 
planet,  has  recommended  Urania. 

On  the  1st  of  September,  1854,  the  thirty-first  asteroid 
was  discovered  at  the  Washington  observatory,  by  Mr. 
James  Ferguson.  It  was  so  close  to  the  planet  Egeria,  of 
which  Mr.  Ferguson  was  in  search,  that  it  was  observed 
along  with  it  on  the  1st.  Another  night's  observation 
proved  that  both  were  planets,  the  new  one  appearing  of 
about  the  same  degree  of  brightness  as  Egeria.  Mr.  Fer- 
guson has  been  employed  for  several  years  with  the  great 
equatorial  telescope  at  Washington,  and  has  spent  a  large 
portion  of  his  time  in  observing  the  places  of  the  newly- 
discovered  asteroids.  This  is  the  only  instance  in  which 
any  American  astronomer  has  been  the  first  discoverer  of 
a  primary  planet.  Mr.  Bond,  of  Cambridge,  was  the  first 
discoverer  of  the  faint  satellite  of  Saturn,  and  several 
American  astronomers  have  enjoyed  the  honor  of  having 
first  discovered  a  comet.  The  honor  of  naming  this  new 
planet  was  left  to  Mr.  Ferguson,  and  he  has  selected  the 
name  of  Euphrosyne.  The  period  of  revolution  appears 
to  be  greater  than  that  of  either  of  the  other  asteroids, 
and  its  inclination  to  the  ecliptic  is  greater  than  any  ex- 
cept Pallas. 

On  the  28th  of  October,  1854,  two  new  asteroids  were 
discovered  at  Paris,  one  of  them  by  M.  Goldschmidt,  the 
other  by  M.  Chacornac.  The  former  appeared  as  a  star 
of  somewhat  less  than  the  tenth  magnitude,  and  has  been 
named  Pomona;  the  latter  somewhat  smaller  than  a 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.     77 

star  of  the  ninth  magnitude,  and  has  been  named 
Poly^mia.  The  eccentricity  of  the  orbit  of  Polymnia  ap- 
pears to  be  greater  than  that  of  any  other  known  member 
of  the  planetary  system,  the  difference  between  the  dis- 
tances from  the  sun  at  perihelion  and  aphelion  amounting 
to  about  the  entire  diameter  of  the  earth's  orbit. 

On  the  evening  of  April  5th,  1855,  M.  Chacornac,  of 
the  Imperial  Observatory  of  Paris,  discovered  another 
small  planet  of  the  eleventh  magnitude.  In  about  two 
hours  its  right  ascension  had  changed  nearly  five  seconds 
of  time,  showing  clearly  its  planetary  character.  On  the 
next  day  the  planet  was  publicly  announced,  and  was 
soon  found  at  the  other  observatories  of  Europe.  This 
planet  has  received  the  name  of  Circe. 

On  the  19th  of  April,  1855,  Dr.  Luther  at  Bilk,  dis- 
covered a  new  planet  of  the  eleventh  magnitude,  and  on 
the  following  day,  the  notice  was  communicated  by  tele- 
graph to  the  editor  of  the  Astronomische  Nachrichten.  On 
the  21st  it  was  detected  both  at  the  Hamburg  and  Bonn 
observatories.  At  the  request  of  the  discoverer,  Dr. 
Peters  and  M.  Kumker  gave  to  the  planet  the  name 
Leucothea,  the  protectress  of  sailors.  This  planet  is  one 
of  the  most  distant  of  the  group  of  asteroids. 

On  the  5th  of  October,  1855,  M.  Goldschmidt  at  Paris, 
discovered  a  new  planet  equal  in  brightness  to  a  star  of 
the  eleventh  or  twelfth  magnitude.  This  new  planet  has 
received  the  name  of  Atalanta,  and  the  eccentricity  of  its 
orbit  appears  to  be  greater  than  that  of  any  other  member 
of  the  planetary  system  except  Polymnia,  and  Leda. 


78  HISTORY  OF  ASTRONOMY. 

On  the  same  evening  with  the  preceding,  and  nearly 
at  the  same  hour,  the  thirty-seventh  asteroid  was  discov- 
ered by  Dr.  Luther  at  Bilk.  It  appeared  like  a  star  of 
the  tenth  magnitude,  and  on  the  following  day  the  dis- 
covery was  communicated  by  telegraph  to  the  editor  of 
the  Nachrichten.  On  the  7th  it  was  seen  both  at  Altona 
and  Hamburg.  This  planet  has  received  the  name  of 
Fides. 

On  the  evening  of  the  12th  of  January,  1856,  M.  Cha- 
cornaCj  at  the  Paris  observatory,  discovered  a  new  planet 
equal  in  brightness  to  a  star  of  the  ninth  or  tenth  magni- 
tude. This  planet  has  received  the  name  of  Leda. 

On  the  8th  of  February,  1856,  M.  Chacornac,  of  the 
Paris  observatory,  discovered  a  new  planet,  being  the 
thirty-ninth  asteroid,  and  equal  to  a  star  of  the  eighth  or 
ninth  magnitude.  This  planet  has  received  the  name  of 
Laetitia. 

On  the  31st  of  March,  1856,  a  new  planet,  being  the  for- 
tieth asteroid,  was  discovered  at  Paris  by  M.  Hermann 
Goldschmidt ;  and  on  the  6th  of  April  it  was  observed 
both  at  Altona  and  Hamburg.  It  appeared  like  a  star  of 
the  ninth  or  tenth  magnitude,  and  has  been  named  Har- 
monia. 

*  On  reviewing  the  preceding  sketch,  we  find  that  Mr. 
Hind,  of  London,  has  been  the  first  discoverer  of  ten  as- 
teroids; M.  de  Gasparis  of  seven;  Mr.  Luther  of  five; 
M.  Chacornac  of  five;  M.  Goldschmidt  of  four;  while 
Olbers  and  Hencke,  have  each  discovered  two.  "We  also 
see  that,  in  several  instances,  the  same  asteroid  has  been 
independently  discovered  by  more  than  one  astronomer. 


ZONE  OF   PLANETS  BETWEEN   MARS  AND  JUPITER.      79 

Among  all  the  astronomers  of  the  present  or  any  former 
age,  Mr.  Hind  stands  pre-eminent  for  his  success  in  the 
discovery  of  new  planetary  bodies.  These  discoveries 
were  all  made  at  the  private  observatory  of  George 
Bishop,  Esq.,  which  was  erected  in  the  year  1836,  in 
Regent's  Park,  London.  The  principal  instrument  of 
this  observatory  is  an  equatorial  telescope,  constructed 
by  Mr.  Dollond,  of  London,  and  equipped  on  the  plan 
known  as  the  English  mounting.  The  solar  focus  of  the 
telescope  is  ten  feet  ten  inches,  and  the  clear  aperture  of 
the  object-glass  seven  inches.  The  circles  are  three  feet 
in  diameter ;  the  hour  circle  reading  by  verniers  to  single 
soconds  of  time,  and  the  declination  circle  to  ten  seconds 
of  arc.  This  instrument  is  driven  by  clock-work;  this 
part  of  the  machinery  in  particular  being  very  elaborately 
worked.  The  telescope  is  provided  with  a  series  of  mag- 
nifying powers  up  to  1200. 

In  the  year  1844,  Mr.  Bishop  secured  the  services  of  J. 
R.  Hind,  Esq.,  then  an  assistant  in  the  magnetical  depart- 
ment of  the  Royal  Observatory,  Greenwich,  where  he 
had  already  distinguished  himself  by  the  zeal  and  ability 
with  which,  in  addition  to  his  ordinary  duties,  which 
were  severe,  he  devoted  himself  to  the  labor  of  ob- 
serving comets,  and  calculating  the  elements  of  their 
orbits. 

Almost  from  the  time  of  Mr.  Hind's  appointment,  the 
observations  took  that  character  for  which  his  talents 
peculiarly  fitted  him,  viz.,  the  search  of  the  heavens  for 
new  comets,  planets,  etc.  His  labors  were  almost  im- 


80  HISTOKY   OF  ASTBONOMY. 

mediately  rewarded  with  success.  Two  comets  were  dis- 
covered in  1846,  and  another  in  1847,  the  latter  of  which 
became  visible  at  noonday,  when  near  its  perihelion, 
and  for  which  the  King  of  Denmark's  gold  medal  was 
awarded. 

The  search  after  small  planets  lying  between  Mars  and 
Jupiter  was  still  more  successful.  His  plan  for  detecting 
them  was  to  observe  and  map  all  the  stars  down  to  the 
eleventh  magnitude  for  several  degrees  on  each  side  of 
the  ecliptic,  and  then  by  a  subsequent  observation  noting 
whether  any  of  them  seemed  to  have  changed  its  place, 
this  being  the  only  planetary  characteristic  observable. 
For  the  discoveries  of  Iris  and  Flora  in  1847,  a  prize  on 
the  Lalande  foundation  was  received  from  the  Academy 
of  Sciences  at  Paris  in  April,  1850  ;  and  in  February,  185% 
he  received  the  gold  medal  of  the  Eoyal  Astronomical 
Society  of  London  for  his  numerous  astronomical  dis- 
coveries, and  in  particular  for  his  discovery  of  eight  small 
planets. 

The  rapid  discovery  of  thirty-six  new  asteroids,  after  a 
barren  interval  of  almost  forty  years  from  the  discovery 
of  Yesta,  is  calculated  to  excite  surprise ;  but  it  is  ex- 
plained by  the  diminutive  size  of  the  new  planets,  and 
the  great  increase  in  the  number  of  observers,  as  well  as 
the  use  of  more  powerful  instruments.  Vesta  appears 
like  a  star  of  the  sixth  magnitude,  Pallas  of  the  seventh, 
while  Ceres  and  Juno  are  of  the  eighth.  Of  the  thirty- 
six  asteroids  more  recently  discovered,  none  of  them,  if 
we  except  perhaps  Iris,  Flora,  and  Laetitia,  are  larger 


ZONE   OF  PLANETS   BETWEEN  MAES  AND  JUPITEK.     81 

than  the  ninth,  magnitude,  while  several  are  as  small  as 
the  tenth,  and  three  or  four  scarcely,  if  ever,  rise  as  high 
as  the  tenth  magnitude.  The  reason  that  Qlbers  was  not 
more  successful  in  his  search  was,  that  he  employed  a 
telescope  of  too  feeble  power,  and  did  not  extend  his  ex- 
amination beyond  stars  of  the  eighth  magnitude. 

Some  may  conclude  that  the  number  of  asteroids  now 
known  is  so  great,  that  the  discovery  of  additional  ones 
is  a  matter  of  no  interest,  and  is  unworthy  the  attention 
of  astronomers.  We  regard  the  question  in  a  very  dif- 
ferent light.  If  only  one  planet  had  hitherto  been  dis- 
covered between  Mars  and  Jupiter,  our  idea  of  the  sim- 
plicity and  perfection  of  the  solar  system  would  have 
been  satisfied,  and  there  might  have  been  found  ingenious 
minds  attempting  to  prove  by  d  priori  reasoning  that  no 
other  planets  could  possibly  exist,  unless  beyond  the 
limits  of  the  orbit  of  Neptune.  But  our  theory  of  the 
solar  system,  although  apparently  simple,  would  not  have 
been  the  true  theory.  Every  new  discovery  shows  the 
solar  system  to  be  more  complex  than  we  had  supposed  ; 
and  unless  we  prefer  error  (provided  it  has  a  show  of 
simplicity)  to  truth,  when  it  appears  to  our  view  complex, 
we  shall  value  every  new  discovery  in  the  solar  system, 
because  it  promises  to  conduct  us  nearer  to  the  true 
theory  of  the  universe.  Every  new  asteroid  which  is 
discovered,  is  a  new  fact  to  be  explained.  It  presents  a 
new  test  by  which  every  theory  is  to  be  tried.  If  our 
theory  be  false,  it  is  probable  that  some  of  these  facts  may 
be  shown  to  be  inconsistent  with  it.  When  the  number 

4* 


82  HISTORY  OF  ASTRONOMY. 

of  known  facts  is  small,  they  may  all  frequently  be  ex- 
plained by  different  and  conflicting  theories.  As  the 
number  of  known  facts  increases,  some  of  them  will 
probably  be  found  inconsistent  with  one  or  the  other  of 
the  theories,  until  at  last  we  reach  a  fact — the  true  experi- 
mentum  crucis — which  is  inconsistent  with  every  theory 
but  one.  Thus  the  true  philosopher,  instead  of  regarding 
the  rapidly  increasing  number  of  asteroids  with  indiffer- 
ence, will  watch  each  new  discovery  with  growing  inter- 
est, in  the  hope  that  it  may  furnish  the  key  to  the  true 
theory  of  the  solar  system. 

The  following  table  exhibits  a  summary  of  the  prin- 
cipal elements  of  forty  asteroids.  Column  first  shows 
the  number  of  each  planet  in  the  order  of  its  dis- 
covery ;  column  second  the  name  of  the  planet ;  column 
third  shows  the  average  distance  from  the  sun  (the  dis- 
tance of  the  earth  from  the  sun  being  taken  as  unity)  ; 
column  fourth  shows  the  number  of  days  required  to 
make  one  revolution  about  the  sun ;  column  fifth  shows 
the  eccentricity  of  the  orbit,  or  the  quantity  by  which  it 
departs  from  the  form  of  a  circle ;  column  sixth  shows 
the  number  of  degrees  by  which  the  plane  of  the  orbit  is 
inclined  to  the  orbit  of  the  earth  ;  column  seventh  shows 
the  position  of  the  line  in  which  the  plane  of  the  orbit 
intersects  the  orbit  of  the  earth;  and  the  last  column 
shows  the  position  of  that  point  of  the  planet's  orbit 
which  is  nearest  the  sun. 

The  existence  of  forty  planets  revolving  round  the  sun 
at  distances  closely  allied  to  each  other,  and  differing 


ZONE   OF  PLANETS  BETWEEN  MARS  AND  JUPITER.     83 


ELEMENTS  OF  THE  ASTEROIDS. 


No. 

NAME. 

§§' 

Time  of 
revolution 
in  days. 

g£ 

v  "3 
o  •-* 

ryi    M 

Inclination, 
of  orbit. 

<3*> 

rti 

3ia 

Long,  of 
perihelion. 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
1.6 
17 
18 
19 
20 
21 
22 
23 
24 
25 
26 
27 
28 
29 
30 
31 
32 
33 
34 
35 
36 
37 
38 
39 
40 

Ceres  ""..... 

2.766 
2.770 
2.668 
2.361 
2.577 
2.425 
2.386 
2.201 
2.386 
3.149 
2.448 
2.335 
2.577 
2.584 
2.643 
2.933 
2.484 
2.294 
2.444 
2.401 
2.434 
2.912 
2.645 
3.144 
2.401 
2.655 
2.347 
2.775 
2.552 
2.366 
3.156 
2.583 
2.866 
2.67S 
2.974 
2.757 
2.654 
2.635 
2.768 
2.254 

1680 
1683 
1592 
1325 
1511 
1379 
1347 
1193 
1346 
2041 
1399 
1303 
1512 
1513 
1570 
1835 
1430 
1269 
1396 
1359 
1387 
1815 
1571 
2037 
1359 
1580 
1313 
1689 
1489 
1329 
2048 
1516 
1772 
1596 
1873 
1672 
1580 
1563 
1682 
1236 

0.079 
.239 
.256 
.090 
.189 
.202 
.231 
.157 
.123 
.101 
.098 
.045 
.085 
.169 
.188 
.131 
.131 
.215 
.159 
.145 
.162 
.104 
.240 
.123 
.253 
.088 
.174 
.155 
.067 
.126 
.216 
.083 
.337 
.114 
.216 
.300 
.180 
.326 
.116 
.289 

11° 
35 
13 
7 
5 
15 
5 
6 
6 
4 
5 
8 
17 
9 
12 
3 
6 
10 
2 
1 
3 
14 
10 
1 
22 

i 

6 
2 
26 
5 
2 
5 
8 
19 
3 
6 
10 
5 

81° 
173 
171 
103 
141 
139 
260 
110 
68 
288 
125 
235 
43 
187 
294 
151 
125 
150 
211 
207 
80 
67 
68 
36 
214 
46 
94 
145 
356 
308 
31 
221 
9 
184 
356 
359 
8 
295 
157 
84 

150° 
122 
54 
251 
136 
15 
41 
33 
72 
227 
317 
302 
120 
179 
28 
11 
259 
16 
31 
99  I 
327  i 
59  j 
123 
135  i 
303 
236 
87 
122 
48 
31 
94 
195 
341 
158 
198 
43 
66 
127 
1 
14  i 

Pallas  

Juno  

Vesta  

Astraea  

Hebe  

Iris..'  

Flora  .  .  . 

Metis  

Hye:eia  . 

Clio  

Egeria  

Eunomia  

Psyche 

Thetis  

Fortuna  

Massilia  

Lutetia  

Calliope  

Thalia  

Themis  

Phocea 

Proserpina  

Euterpe     .  . 

Amphitrite     

Urania 

Euphrosyne  

Pomona  ...        .        . 

Polymnia  

Circe  

Atalanta  ... 

Fides  

Leda  

Laetitia  

Harmonia.                   . 

from  all  the  other  planets  in  their  diminutive  size,  is  one 
of  the  most  singular  phenomena  in  our  solar  system. 


84  HISTORY    OF  ASTRONOMY. 

This  fact  will  appear  the  more  striking  if  we  draw  a 
diagram  representing  the  orbits  of  all  the  known  planets 
in  their  proper  proportions.  We  shall  find  that  while 
the  orbits  of  Mercury,  Venus,  the  Earth,  and  Mars  are 
quite  detached  from  each  other,  and  the  orbits  of  Jupiter, 
Saturn,  Uranus,  and  Neptune  are  separated  by  intervals 
which  the  imagination  can  with  difficulty  grasp,  between 
Mars  and  Jupiter  is  a  cluster  of  bodies  whose  orbits  are  so 
interlaced  as  to  suggest  the  apprehension  of  frequent  and 
inevitable  collision. 

The  diagram  on  the  following  page  represents  the  or- 
bits of  nine  of  these  small  planetary  bodies,  designed  to 
be  selected  so  as  to  afford  a  tolerable  specimen  of  the 
whole.  The  other  thirty-one  orbits  are  omitted,  to  avoid 
the  confusion  of  so  many  lines  in  a  single  diagram.  In 
one  respect  this  representation  is  calculated  to  convey  an 
erroneous  impression.  All  the  orbits  are  represented  as 
situated  in  the  same  plane,  whereas,  in  reality,  no  two  of 
them  are  situated  in  the  same  plane.  These  planes  all 
pass  through  the  sun,  and  are  inclined  to  the  earth's  orbit 
in  angles  indicated  in  column  sixth  of  the  preceding 
Table.  One  half  of  each  orbit  must  therefore  be  below 
the  earth's  orbit,  and  the  other  half  above  it ;  and  in  order 
to  indicate  as  fully  as  possible  the  actual  position  of  these 
orbits,  the  portion  which  falls  below  the  plane  of  the 
earth's  orbit  is  indicated  by  a  dotted  line,  while  the  re- 
mainder is  indicated  by  a  continuous  black  line.  These 
orbits,  then,  do  not  really  intersect  each  other  as  repre- 
sented in  the  diagram.  Indeed,  no  two  of  the  planetary 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.      85 

orbits  intersect,  although  some  of  them  approach  within 
moderate  distances  of  each  other.  The  orbit  of  Fortuna 
approaches  the  orbit  of  Metis  within  less  than  the  Moon's 
distance  from  the  earth.  The  orbit  of  Massilia  approaches 
almost  equally  near  the  orbit  of  Astrsea,  and  the  orbit  of 
Lutetia  to  that  of  Juno. 


PLAJfETAEY    ORBITS. 


It  is  evident,  then,  at  a  glance,  that  these  forty  small 
planets  sustain  to  each  other  a  relation  different  from  that 
of  the  other  members  of  the  solar  system.  We  see  a 


86  HISTORY  OF  ASTRONOMY. 

family  likeness  running  through  the  entire  group,  and  it 
naturally  suggests  the  idea  of  a  common  origin.  This 
idea,  as  has  been  already  stated,  occurred  to  the  mind  of 
Olbers  after  the  discovery  of  the  second  asteroid,  and  led 
to  his  celebrated  theory  that  all  these  bodies  originally 
constituted  a  single  planet  which  had  been  broken  into 
fragments  by  the  operation  of  some  internal  force.  Have 
we  any  means  of  testing  the  soundness  of  this  theory  ? 

If  the  earth  should  be  broken  into  fragments  by  the 
operation  of  some  internal  force  (such,  for  example,  as 
that  which  causes  the  eruption  of  a  volcano,)  the  frag- 
ments might  be  projected  in  various  directions,  and  with 
very  unequal  velocities ;  but  each  would  describe  an 
ellipse  of  which  the  sun  would  occupy  one  of  the  foci — 
if  we  except  the  extreme  but  possible  case  of  a  fragment 
projected  with  such  a  velocity  as  to  carry  it  beyond  the 
limit  of  the  sun's  attraction.  Leaving  out  of  view  the 
disturbance  arising  from  the  mutual  attraction  of  the 
planets,  which  produces  only  minute  effects,  each  frag- 
ment would  continue  to  describe  the  same  ellipse  in  its 
successive  revolutions  about  the  sun ;  in  other  words, 
these  ellipses  would  all  have  a  common  point  of  intersection. 
The  same  conclusion  must  hold  true  for  the  asteroids, 
according  to  the  theory  of  Olbers.  The  question  then 
arises,  have  the  orbits  of  the  asteroids  a  common  point 
of  intersection  ?  A  single  glance  at  the  above  diagram 
will  settle  this  question  in  the  negative.  But  Olbers 
replies  that  the  orbits  of  the  planets  are  disturbed  by 
their  mutual  attractions.  These  orbits  should  originally 


ZONE   OF  PLANETS  BETWEEN  MAES  AND- JUPITER.      87 

have  had  a  common  point  of  intersection,  but  at  each 
revolution  they  suffer  a  slight  displacement,  until,  in  the 
lapse  of  time,  the  position  of  the  orbits  has  become  so 
completely  changed  as  to  show  scarcely  a  trace  of  their 
original  intersection.  Is  such  a  result  possible  ?  A  few 
simple  considerations  will  satisfy  us  that  if  the  orbits  of 
the  asteroids  ever  had  a  common  point  of  intersection, 
such  a  result  must  have  belonged  to  a  period  of  time 
indefinitely  remote. 

The  line  in  which  the  plane  of  the  planet's  orbit  in- 
tersects some  other  plane  selected  for  common  reference 
is  called  technically  the  line  of  the  nodes.  If  the  asteroid 
orbits  had  ever  a  common  point  of  intersection,  all  the 
nodal  lines  upon  one  of  the  orbits  must  have  coincided. 
Now,  as  two  of  the  asteroid  orbits  are  inclined  less  than 
one  degree  to  the  earth's  orbit,  we  will,  for  greater  con- 
venience, employ  the  latter  as  the  plane  of  reference. 
By  referring  to  our  table  on  page  83,  it  will  be  seen  that 
the  ascending  nodes  of  the  asteroids  are  distributed, 
though  unequally,  through  the  four  quadrants  of  the 
circle.  Twelve  of  them  lie  in  the  first  quadrant,  thirteen 
in  the  second,  eight  in  the  third,  and  seven  in  the 
fourth.  The  nodes  of  all  the  planetary  orbits  are  in 
constant  motion,  but  the  motion  for  a  single  year  is 
extremely  small.  The  animal  motion  of  the  node  of 
Mercury  is  ten  seconds  ;  that  of  Yenus  twenty  seconds ; 
Mars  twenty -five  seconds,  etc.  The  nodes  of  the  aster- 
oids, as  far  as  the  computation  has  been  made,  move  at 
somewhat  similar  rates;  the  most  rapid  motion  known 


88  HISTOEY  OF  ASTKONOMY. 

being  about  fifty  seconds  a  year.  If  we  suppose  the 
nodal  lines  of  all  these  orbits  to  move  steadily  toward 
each  other,  it  would  require  in  some  of  them  a  motion  of 
fifty  seconds  a  year,  continued  for  more  than  6000  years, 
to  bring  them  to  a  coincidence. 

It  should  also  be  observed,  that  not  only  must  the 
nodes  of  all  the  asteroids  coincide,  but  the  distance  of 
the  planets  from  the  sun  must  be  the  same  at  that  instant. 
Now  the  distances  of  these  planets  from  the  sun,  when  at 
their  nodes,  differ  by  more  than  a  hundred  millions  of 
miles ;  so  that  to  bring  .them  all  together  requires  some- 
thing more  than  a  change  in  the  position  of  the  nodes. 
"We  may  bring  about  a  coincidence,  in  the  case  of  some 
of  the  asteroids,  by  supposing  the  longer  diameter  of  the 
elliptic  orbit  to  change  its  position  in  the  plane  of  the 
orbit.  Such  a  change  does  really  take  place  in  the  case 
of  every  planetary  orbit,  but  with  none  of  the  larger 
planets  does  it  exceed  twenty  seconds  a  year.  This  mo- 
tion for  the  asteroids,  so  far  as  it  has  been  computed,  is 
somewhat  more  rapid,  amounting,  in  one  instance,  to 
seventy  seconds  a  year ;  but  even  with  this  motion,  it 
would  require  the  lapse  of  five  thousand  years  to  bring 
about  an  intersection  in  the  case  of  many  of  the  asteroid 
orbits.  "When  now  it  is,  remembered,  that  in  order  to 
give  a  common  point  of  intersection  to  these  forty  orbits, 
all  the  nodal  lines  upon  one  of  the  orbits  must  coincide, 
and  at  the  same  instant  all  the  distances  from  the  sun 
must  be  equal  to  each  other,  we  must  be  prepared  to 


ZONE  OF  PLANETS  BETWEEN  MARS  AND    JUPITER.     89 

admit  that  such  an  occurrence  could  only  have  taken 
place  myriads  of  years  ago. 

The  preceding  difficulties,  however,  are  small  in  com- 
parison with  another  which  remains  to  be  stated.  The 
orbit  of  Hygeia  completely  incloses  the  orbit  of  Flora 
(and  indeed  several  other  orbits),  and  would  still  inclose 
them,  although  the  greater  diameter  of  each  of  them 
were  revolved  through- an  entire  circumference,  since  the 
least  distance  of  Hygeia  from  the  sun  exceeds  the  greatest 
distance  of  Flora.  The  same  is  true  of  Themis,  as  com- 
pared with  Flora  and  several  other  orbits.  The  least 
distance  of  Hygeia  from  the  sun  exceeds  the  greatest 
distance  of  Flora  by  more  than  twenty-five  millions  of 
miles.  In  order  to  render  an  intersection  of  these  orbits 
possible,  we  must  suppose  a  great  variation  of  the  ec- 
centricity. But  the  change  of  the  eccentricity  of  the 
planetary  orbits  is  exceedingly  slow,  and  the  present  rate 
of  increase  of  the  eccentricity  of  Yesta  must  be  con- 
tinued twenty-seven  thousand  years  to  render  the  aphelion 
distance  of  that  planet  equal  to  the  perihelion  distance 
of  Hygeia.  Moreover,  the  eccentricity  of  the  orbit  of 
Yesta  is  now  increasing,  which  implies  that  in  past  ages 
the  interval  between  Yesta  and  Hygeia  must  have  been 
greater  than  it  is  at  present;  whence  the  conclusion 
seems  irresistible,  that  the  orbits  of  Yesta  and  Hygeia 
can  not  have  intersected  for  several  myriads  of  years. 
When  the  secular  variations  of  the  elements  of  each  of 
the  asteroids  have  been  computed,  astronomers  will  be 
able  to .  assign  a  limit  of  time  beyond  which  the  inter- 


90  HISTOEY  OF  ASTKONOMY. 

section  of  all  the  asteroid  orbits  must  have  occurred,  if, 
indeed,  such  an  intersection  ever  took  place.  The  dis- 
covery of  many  of  these  bodies  is  so  recent  that,  as  yet, 
there  has  not  been  sufficient  time  for  such  a  computa- 
tion ;  but,  from  what  we  already  know,  we  hazard  little 
in  venturing  the  opinion  that,  when  this  computation 
shall  be  made,  it  will  appear,  that  if  the  asteroid  planets 
ever  composed  a  single  body  which  exploded,  as  Gibers 
supposed,  such  explosion  must  have  occurred  myriads  of 
years  ago.  Indeed,  the  discovery  of  such  a  host  of  aster- 
oids seems  to  have  stripped  the  theory  of  Olbers  of 
nearly  all  the  plausibility  it  possessed  when  it  was  orig- 
inally proposed ;  and  it  would  seem  hardly  less  reason- 
able to  suppose  that  the  Earth  and  Yenus  originally  con- 
stituted one  body,  than  to  admit  the  same  for  the  forty 
asteroids. 

But  if  we  reject  the  theory  of  Olbers,  what  do  we 
conclude  ?  That  the  asteroids  bear  no  special  relation- 
ship to  each  other  ?  Do  they  not  all  clearly  indicate  a 
family  resemblance  ?  And  if  so,  how  do  we  account  for 
this  relationship? 

There  are  several  reasons  for  believing  in  some  pe- 
culiar relationship  between  the  asteroids. 

1.  Unlike  the  other  planets  of  our  system,  they  are 
all  of  diminutive  size — the  largest  of  them  hardly  ex- 
ceeding one  or  two  hundred  miles  in  diameter.  M.  Le 
Yerrier,  after  a  close  examination  of  the  nature  and 
amount  of  the.  influences  exerted  by  the  entire  group 
of  asteroids  upon  the  nearer  planets,  Mars  and  the  Earth, 


ZONE   OF  PLANETS  BETWEEN   MARS  AND  JUPITER.      91 

has  arrived  at  the  conclusion  that  the  sum  total  of  the 
matter  constituting  the  small  planets  situated  between 
the  mean  distances  2*20  and  3*16  (including  undiscovered 
as  well  as  known  asteroids),  can  not  exceed  about  one 
fourth  of  the  mass  of  the  earth. 

2.  The  asteroids  in  their  position  occupy  a  zone  en- 
tirely distinct  from  the  other  planets  of  the  solar  system. 
Between  the  orbits  of  Jupiter  and  Saturn — between 
Saturn  and  Uranus — is  an  immense  interval,  furnishing 
space  enough  for  a  host  of  little  bodies  to  circulate  around 
the  sun  ;  but  in  not  a  solitary  instance  has  any  such  body 
been  found,  except  between  Mars  and  Jupiter.  Some 
may  attempt  to  account  for  this  circumstance  by  saying 
that  astronomers  have  long  been  watching  exclusively 
this  portion  of  space,  and  have  left  all  other  regions 
entirely  unexplored.  An  exploration,  conducted  upon 
such  a  principle,  is  simply  a  physical  impossibility.  If 
there  were  a  small  planet  between  the  Earth  and  Mars, 
it  would  have  stood  the  same  chance  of  detection,  in  the 
explorations  of  the  past  ten  years,  as  if  it  were  situated 
between  Mars  and  Jupiter;  and,  indeed,  it  would  have 
stood  a  better  chance  of  detection,  inasmuch  as  it  would 
appear  of  greater  brightness  on  account  of  its  proximity 
to  us.  If  there  were  a  small  planet  circulating  between 
Jupiter  and  Saturn,  it  would  have  stood  the  same  chance 
of  detection  as  if  it  had  been  placed  this  side  of  Jupiter, 
except  that  it  would  appear  somewhat  fainter  on  account 
of  its  increased  distance.  The  fact  that  we  have  dis- 
covered forty  small  planets  between  Mars  and  Jupiter, 


92  HISTORY  OF  ASTKONOMY. 

and  not  a  solitary  one  in  any  other  portion  of  the  solar 
system,  points  to  something  special  in  this  region  of  the 
heavens.  In  other  words,  we  have  discovered  a  limited 
zone  of  little  planetary  bodies,  and  have  not  been  able 
to  discover  a  single  body  of  the  same  class  situated  out 
of  this  zone. 

3.  The  orbits  of  these  little  bodies  present  some  special 
peculiarities. 

If  we  refer  to  the  table  on  page  83,  we  shall  perceive 
that  the  perihelia  of  the  orbits  are  not  distributed  uni- 
formly through  the  zodiac.  In  the  first  quarter  of  the 
zodiac  we  find  seventeen  perihelia,  in  the  second  quarter 
twelve,  in  the  third  quarter  six,  and  in  the  fourth  quarter 
five.  The  ascending  nodes  of  the  orbits  are  distributed 
with  greater  uniformity.  Thus,  in  the  first  quadrant 
we  find  twelve  nodes,  in  the  second  thirteen,  in  the  third 
eight,  and  in  the  fourth  seven. 

The  greatest  inclination  in  the  case  of  any  of  the  larger 
planets  is  seven  degrees ;  but  the  inclinations  of  the 
orbits  of  the  asteroids  range  from  near  zero  to  thirty- 
five  degrees,  the  inclination  of  seventeen  of  the  orbits 
exceeding  seven  degrees.  The  greatest  eccentricity  in  the 
case  of  any  of  the  large  planets  is  one  fifth ;  but  the 
eccentricities  of  the  orbits  of  the  asteroids  range  from 
near  zero  to  one  third. 

4.  But  the  most  striking  peculiarity  of  these  orbits  is, 
that  they  all  lock  into  one  another  like  the  links  of  a 
chain,  so  that  if  the  orbits  are  supposed  to  be  represented 
materially  as  hoops,  they  all  hang  together  as  one  system. 


ZONE   OF  PLANETS  BETWEEN  MARS  AND  JUPITER.      93 

The  orbits  of  Hygeia  and  Themis,  being  the  largest  of 
all  the  orbits,  completely  inclose  nearly  all  of  them,  and 
lock  into  but  a  small  number ;  while  the  orbits  of  Mas- 
silia,  Astraea,  Pallas,  etc.,  lock  into  nearly  all  of  the 
orbits ;  so  that  if  we  take  hold  of  the  orbit  of  Hygeia 
(supposed  to  be  a  material  hoop),  it  will  support  the 
orbits  of  Iris,  Thalia,  Calliope,  and  two  or  three  others, 
while  these  in  turn  lock  into  and  support  all  the  rest. 
Indeed,  if  we  seize  hold  of  any  orbit  at  random,  it  will 
drag  all  the  other  orbits  along  with  it.  This  feature  of 
itself  sufficiently  distinguishes  the  asteroid  orbits  from  all 
the  other  orbits  of  the  solar  system. 

If  we  reject  the  theory  that  these  asteroids  were 
originally  united  in  one  solid  body,  it  seems  nevertheless 
difficult  to  avoid  the  conclusion  that  similar  causes  have 
operated  in  determining  the  orbits  of  this  zone  of  planets. 
It  is  impossible  to  assign  any  cause  for  these  resem- 
blances without  adopting  some  theory  respecting  the  origin 
of  the  solar  system.  The  theory  of  gradual  condensa- 
tion, as  developed  by  Laplace  in  the  nebular  hypothesis, 
affords  at  least  a  plausible  explanation  of  these  phe- 
nomena. 

Laplace  supposed  that  the  matter  composing  the  bodies 
of  our  solar  system  originally  existed  in  the  condition  of 
an  immense  nebula,  extending  beyond  the  limits  of  the 
most  distant  planet — that  this  nebulous  mass  had  an  ex- 
ceedingly elevated  temperature,  and  a  slow  rotation  on 
its  axis — that  the  nebula  gradually  cooled ;  and  as  it  con- 
tracted in  dimensions,  its  velocity  of  rotation,  according 


94  HISTORY  OF  ASTRONOMY. 

to  the  principles  of  mechanics,  increased,  until  the  cen- 
trifugal force  arising  from  the  rotation  became  equal  to 
the  attraction  of  the  central  mass  for  the  exterior  zone, 
when  this  zone  necessarily  became  detached  from  the 
central  mass.  As  the  central  mass  continued  to  contract 
in  its  dimensions,  and  its  velocity  of  rotation  continued  to 
increase,  the  centrifugal  force  again  became  equal  to  the 
attraction  of  the  central  mass  for  the  exterior  zone,  and  a 
second  zone  was  detached.  Thus,  a  number  of  zones  of 
nebulous  matter  were  successively  detached?  until,  by 
condensation,  the  central  mass  became  of  comparatively 
small  dimensions  and  great  density. 

The  zones  thus  successively  detached  would  form  con- 
centric rings  of  vapor,  all  revolving  in  the  same  direction 
round  the  sun.  If  the  particles  of  each  ring  continued  to 
condense  without  separating  from  each  other,  they  would 
ultimately  form  a  liquid  or  a  solid  ring.  But  generally 
each  ring  of  vapor  would  break  up  into  separate  masses, 
revolving  about  the  sun  with  velocities  slightly  differing 
from  each  other.  These  masses  would  assume  a  spheroidal 
form ;  that  this,  they  would  form  planets  in  the  state  of 
vapor.  But  if  one  of  these  masses  was  large  enough  to 
attract  each  of  the  others  in  succession  to  itself,  the  ring 
of  vapor  would  be  converted  into  a  single  spheroidal 
mass  of  vapor,  and  we  should  have  a  single  planet  of 
great  mass  for  each  zone  of  vapor  detached.  But  if  no 
one  of  these  masses  had  a  preponderating  size,  they  would 
all  continue  to  revolve  about  the  sun  in  independent 
orbits,  and  would  form  a  zone  of  little  planets,  such 


ZONE  OF  PLANETS  BETWEEN  MARS  AND  JUPITER.      95 

as  we  have  actually  discovered  between  Mars  and  Ju- 
pitec, 

"With  regard  to  the  actual  number  of  bodies  belonging 
to  this  zone  of  planets,  we  can  do  little  more  than  con- 
jecture. Already  we  have  one  asteroid  of  the  sixth 
magnitude,  one  of  the  seventh,  five  of  the  eighth,  nineteen 
of  the  ninth,  and  fourteen  of  the  tenth  or  eleventh. 
It  would  require  400  bodies  as  large  as  the  largest  of 
the  asteroids  to  make  a  body  one  fourth  of  the  size  of  the 
earth ;  and,  according  to  Le  Yerrier,  the  sum  of  all  the 
asteroids  can  not  exceed  this  limit.  When  we  consider 
the  shortness  of  the  period  during  which  stars  below  the 
eighth  magnitude  have  been  systematically  observed,  we 
see  room  for  the  discovery  of  several  more  planets  of  the 
ninth  magnitude,  and  perhaps  three  or  four  hundred  more 
of  inferior  dimensions. 


SECTION    III. 

THE  DISCOVERY  OF  AN  EIG-HTH  SATELLITE  OF  SATURN. 

SATURN  has  long  been  known  to  be  attended  by  seven 
satellites.  "If  we  number  these  satellites  in  the  order  of 
their  distances  from  the  primary,  the  sixth  was  discovered 
by  Huygens  in  1655,  the  seventh  by  Cassini  in  1671,  the 
fifth  by  the  same  in  1672,  the  third  and  fourth  also  by 
Cassini  in  1684.  The  first  and  second  were  discovered 
by  Dr.  Herschel  in  1789.  The  five  satellites  first  dis- 
covered may  be  seen  by  a  ten  feet  achromatic ;  but  the 
two  interior  satellites  can  only  be  seen  by  a  very  power- 
ful telescope.  Sir  John  Herschel,  at  the  Cape  of  Good 
Hope,  in  1836  and  1837,  repeatedly  observed  the  second 
satellite  with  his  reflector  of  18  inches  aperture ;  and  in 
one  instance  only,  he  caught  a  glimpse  of  a  point  of  light, 
which  he  suspected  to  be  the  first  satellite.  Mr.  Lassell, 
with  his  large  reflector,  obtained  three  observations  of  the 
first  satellite,  in  1846.  Sir  John  Herschel  has  proposed 
to  distinguish  these  satellites  by  proper  names,  as  fol- 
lows : — 

1.  Mimas,  which  makes  its  revolution  in  Od.  22h.  36m. 


2.  Enceladus, 

3.  Tethys, 

4.  Dione, 
6.  Rhea, 

6.  Titan, 

7.  lapetus, 


1  8  53 

1  21  18 

2  17  44 
4  12  25 

15  22  41 

79  7  54 


EIGHTH  SATELLITE   OF   SATUKN.  97 

During  the  year  1848,  this  planet  was  subjected  to  the 
most  rigid  scrutiny,  in  consequence  of  the  disappearance 
of  its  ring,  it  being  presented  edgewise  to  the  sun ;  and 
on  the  16th  of  September,  an  eighth  satellite  was  dis- 
covered by  the  Messrs.  Bond  of  Cambridge,  Mass.  The 
following  is  Mr.  Bond's  account  of  the  discovery.  "  On 
the  evening  of  September  16th,  we  noticed  a  small  star 
situated  nearly  in  the  plane  of  Saturn's  ring,  and  between 
the  satellites  Titan  and  lapetus.  This  circumstance  was 
at  that  time  regarded  as  accidental;  nevertheless,  the 
position  of  the  star,  with  respect  to  Saturn,  was  recorded. 
The  next  night  favorable  for  observation  was  the  18th. 
While  comparing  the  relative  brightness  of  the  satellites, 
we  again  noticed  the  same  object,  similarly  situated  with 
respect  to  the  planet,  and  we  carefully  observed  its  posi- 
tion. But  up  to  this  moment,  its  real  nature  was  scarcely 
suspected.  Measures,  carefully  made  during  the  evening 
of  the  19th,  having  proved  that  the  star  partook  of  the 
retrograde  motion  of  Saturn,  we  studied  that  part  of  the 
heavens  toward  which  the  planet  was  moving.  Each  of 
the  stars  which  it  was  expected  to  approach  during  the 
two  following  nights  was  marked  upon  a  chart,  and 
micrometric  measurements  fixed  its  position  and  distance 
with  respect  to  neighboring  objects. 

"The  evening  of  the  20th  was  cloudy. 

"  On  the  21st  the  new  satellite  had  approached  the 
planet,  and  it  sensibly  changed  its  position  with  respect  to 
the  stars  during  the  time  of  observation.  Similar  obser- 
vations were  repeated  on  the  nights  of  the  22d  and  23d." 

5 


98  HISTOKY  OF  ASTRONOMY. 

On  the  18th  of  September,  the  same  object  was  ob- 
served by  Mr.  Lassell,  of  Liverpool.  The  following  is 
Mr.  Lassell's  account  of  the  discovery.  "  On  the  18th, 
while  I  was  attentively  examining  the  planet  Saturn,  I 
was  struck  with  the  appearance  of  two  stars  situated  on 
the  line  of  the  interior  satellites.  I  supposed  that  one  of 
them,  which  I  shall  designate  by  c,  was  the  most  distant 
satellite,  and  the  other,  which  I  shall  designate  by  x,  a 
fixed  star.  In  order  to  prepare  myself  for  the  subsequent 
observations,  I  made  a  careful  map  of  its  position  with  re- 
spect to  some  fixed  stars  in  its  vicinity,  one  of  which  I 
shall  designate  by  a. 

"  On  the  19th  I  was  surprised  to  find  that  the  two 
stars,  c  and  x,  already  mentioned,  had  receded  from  the 
fixed  star  a,  x  remaining  exactly  on  the  line  of  the  satel- 
lites, but  appearing  to  have  approached  the  planet ;  while 
c,  although  it  followed  Saturn,  had  passed  to  the  north  of 
the  plane  of  the  orbits  of  the  interior  satellites. 

"  This  appearance  suggested  the  idea  that  x  must  be  a 
new  satellite,  and  c  lapetus.  In  order  to  verify  this  con- 
jecture, I  took  the  difference  of  right  ascension  between 
x  and  a,  and  between  c  and  a.  The  result  showed  that 
in  2h.  36m,  x  had  moved  to  the  west  of  a  by  2s.  47 :  and 
that  in  Ih.  24m,  c  had  moved  Is.  27  to  the  west  of  a ; 
which  clearly  proves  that  the  two  stars  x  and  c  were  in 
motion.  I  measured  twice  at  an  interval  of  four  hours, 
the  distance  of  x  from  the  line  passing  through  the  in- 
terior satellites,  and  satisfied  myself  that  during  this  in- 
terval, the  distance  experienced  no  sensible  change.  As 


EIGHTH  SATELLITE  OF  SATURN.  99 

the  motion  of  Saturn  toward  the  south  was  IS"  in  4 
hours,  it  would  plainly  have  left  the  point  x  behind,  if  it 
had  been  a  fixed  star.  The  conclusion  is  inevitable ;  x 
is  a  satellite  hitherto  undiscovered.  This  is  explained  by 
its  being  a  very  faint  object,  even  in  my  telescope  of  24 
inches  aperture;  and  it  may  experience  variations  of 
light,  which  render  it  invisible  in  some  parts  of  its  orbit. 

"  I  obtained  two  other  observations  of  the  satellite  on 
the  21st  and  22d.  In  the  former  case,  the  elongation  to 
the  east  of  the  planet  was  3'  54";  and  in  the  latter  3'  27" ; 
the  star  followed  sensibly  the  line  of  the  interior 
satellites." 

Thus  it  appears  that  a  most  important  discovery  was 
made  independently  and  almost  simultaneously  on  op- 
posite sides  of  the  Atlantic — but  Mr.  Bond  has  an 
unequivocal  priority  of  two  days.  This  is  the  first  ad- 
dition to  our  planetary  system  made  by  an  American 
astronomer.  The  orbit  of  the  new  satellite  lies  between 
Titan  and  lapetus,  and  serves  to  fill  up  a  large  chasm 
before  existing.  It  is  fainter  than  either  of  the  two 
interior  satellites  discovered  by  Sir  William  Herschel. 
Its  time  of  revolution  is  about  21d.  4h.  20ra. ;  its  semi- 
axis  at  the  mean  distance  of  Saturn  214",  indicating  a 
real  distance  of  about  940.000  miles,  and  Messrs.  Bond 
and  Lassell  have  concurred  in  giving  it  the  name  of 
Hyperion. 

It  will  be  observed  that  there  is  still  a  large  gap 
between  Hyperion  and  lapetus,  rendering  it  not  improb- 
able that  other  satellites  yet  remain  to  be  discovered. 


SECTION  IV. 

ON  THE  SATELLITES  OF  URANTJS. 

UKANUS  was  discovered  to  be  a  planet  by  Sir  William 
Herschel  in  1781,  and  in  1787  he  discovered  two  satellites, 
wliose  periods  were  satisfactorily  determined  by  his  sub- 
sequent observations.  In  1797  he  announced  the  dis- 
covery of  four  additional  satellites,  viz.,  one  within  the 
orbits  of  both  the  former  two  ;  one  intermediate  between 
the  two;  and  two  exterior  to  both  of  them,  but  the 
periods  of  these  satellites  he  acknowledged  to  be  very 
uncertain.  In  his  last  paper  on  this  subject,  commu- 
nicated to  the  Eoyal  Society  in  1815,  he  says,  "that  there 
are  additional  satellites,  besides  the  two  principal  larger 
ones,  I  can  have  no  doubt ;  but  to  determine  their  number 
and  situation,  will  probably  require  an  increase  of  illum- 
inating power  in  our  telescopes." 

In  1834,  Sir  John  Herschel  published  a  paper  contain- 
ing a  thorough  discussion  of  his  father's  observations, 
together  with  his  own,  upon  the  two  satellites  first  dis- 
covered ;  and  he  adds,  "  of  other  satellites  than  these 
two,  I  have  no  evidence." 

In  the  year  1838,  Dr.  Lamont,  of  Munich,  published  a 
few  observations  of  the  two  brighter  satellites  of  Uranus, 
and  states  that  he  had  seen  only  one  additional  satellite, 


ON  THE  SATELLITES  OF   URANUS.  101 

and  that  but  in  a  single  instance.  This  satellite  he  con- 
sidered to  be  the  most  remote  "of  the  six  enumerated  by 
Herschel. 

With  the  exception,  therefore,  of  the  solitary  observa- 
tion of  Dr.  Lament,  the  only  evidence  we  have  had  (until 
recently)  of  the  existence  of  more  than  two  satellites 
of  Uranus  was  derived  from  the  observations  of 
Sir  William  Herschel ;  and  he  would  not  pronounce  a 
decided  opinion  as  to  their  number  or  their  periods  of 
revolution. 

At  last,  in  the  autumn  of  1847,  Mr.  Lassell,  of  Liver- 
pool, and  M.  Struve,  at  Pulkova,  obtained  unequivocal 
evidence  of  the  existence  of  a  third  satellite.  The  orbit 
of  this  satellite  was  evidently  smaller  than  that  of  either  of 
the  two  bright  ones ;  yet  the  period  indicated  by  LasselTs 
observations  did  not  agree  with  that  deduced  by  Struve  ; 
and  both  differed  from  the  interior  satellite  of  Sir 
William  HerscheL  While  Lassell's  observations  in- 
dicated a  period  of  about  two  days,  Struve  deduced 
from  his  observations  a  period  of  four  days;  and  the 
time  assigned  by  Herschel  to  his  interior  satellite  was 
nearly  six  days.  Thus  the  question  seemed  involved  in 
total  confusion,  and  the  honest  enquirer  might  well  be 
puzzled  to  decide  whether  there  existed  three  satellites, 
or  only  one,  interior  to  the  two  brighter  ones. 

In  the  autumn  of  1851,  Mr.  Lassell  succeeded  in 
settling  this  vexed  question.  On  ten  different  nights  in 
the  months  of  October,  November  and  December,  he  saw 
simultaneously  four  satellites,  and  recorded  their  positions. 


102  HISTOEY  OF  ASTRONOMY. 

The  intervals  were  so  short  as  to  enable  him  to  identify 
each  satellite  without  danger  of  mistake.  These  sat- 
ellites were  the  two  brighter  ones  discovered  by  Her- 
schel,  and  two  interior  ones,  whose  periods  are  about 
two  and  four  days  respectively. 

In  the  autumn  of  1852,  Mr.  Lassell  transported  his 
telescope  to  the  island  of  Malta,  in  the  Mediterranean, 
for  the  purpose  of  securing  the  advantage  of  a  lower 
latitude  and  a  purer  sky,  and  here  he  succeeded  in  obtain- 
ing a  very  complete  series  of  observations  of  the  satellites 
of  Uranus.  The  nearest  satellite  was  observed  on  24 
different  nights ;  the  second  satellite  on  23  nights ;  and 
the  two  brighter  satellites  on  26  nights.  By  combining 
these  observations  with  those  of  1847  and  1851,  we  are 
able  to  assign  the  dimensions  of  their  orbits  and  their 
periods  of  revolution  with  great  precision.  The  period 
of  the  nearest  satellite  is  2.520345  days  ;  or  2d.  12h.  29m. 
20s.  66.  The  period  of  the  second  satellite  is  4.144537 
days;  or  4d.  3h.  28m.  8s.  00. 

From  the  combination  of  all  the  observations  between 
1787  and  1848,  Mr.  Adams  has  determined  the  period 
of  the  third  satellite  to  be  8d.  16h.  56m.  24s.  88  ;  and  in 
the  same  manner  he  has  determined  the  period  of  the 
fourth  satellite  to  be  13d.  llh.  6m.  55s.  21. 

Let  us  now  examine  the  observations  of  Sir  William 
Herschel,  and  see  what  light  is  shed  upon  them  by  the  in- 
formation recently  obtained.  There  are  four  instances 
in  which  he  observed  what  he  called  "an  interior 
satellite." 


ON  THE  SATELLITES  OF   URANUS.  103 

On  the  18th  of  January,  1790,  he  recorded  an  object 
"excessively  faint,  and  only  seen  by  glimpses — two 
diameters  of  the  planet  following." 

On  the  27th  of  March,  1794,  he  recorded  as  follows : 
"  I  had  many  glimpses  of  small  stars  or  supposed  satel- 
lites, but  not  one  of  them  could  I  see  for  any  constancy. 
They  were  only  lucid  glimpses." 

On  the  15th  of  February,  1798,  an  interior  satellite 
was  seen  about  its  greatest  northern  elongation,  between 
the  planet  and  the  second  satellite.  On  the  16th  the 
place  where  the  satellite  had  been  the  day  before  was 
scrupulously  examined,  and  as  there  was  no  star  remain- 
ing in  that  place,  the  removal  of  the  interior  satellite 
from  its  former  position  was  ascertained. 

On  the  17th  of  April,  1801,  the  interior  satellite  was 
seen  about  its  greatest  southern  elongation.  On  the  fol- 
lowing night,  no  star  was  visible  in  the  same  position. 

It  must  be  considered  doubtful  whether  in  1790  and 
1794,  Sir  William  Herschel  really  saw  an  interior  satel- 
lite. The  observations  of  1798  and  1801  appear  to  be 
more  reliable;  but  the  interval  between  these  ob- 
servations does  not  correspond  very  well  with  the  motion 
of  either  the  first  or  second  satellite  of  Lassell.  It  is 
possible  that  one  of  these  observations  may  have  been 
made  upon  the  first  satellite,  and  the  other  upon  the 
second. 

In  one  instance  Sir  William  Herschel  saw  what  he 
called  an  intermediate  satellite. 

On  the  26th  of  March,  1794,  a  supposed  satellite  was 


104  HISTORY   OF  ASTRONOMY. 

seen  more  than  two  hours.  On  the  following  evening 
it  was  gone  from  the  place  where  he  had  seen  it  the 
night  previous. 

There  are  five  instances  in  which  Herschel  observed 
what  he  called  "  an  exterior  satellite." 

On  the  9th  of  February,  1790,  a  supposed  third  satel- 
lite was  remarked  in  a  line  with  the  planet  and  the 
second  satellite,  and  about  twice  the  distance  of  the 
second  satellite.  On  the  12th  the  supposed  satellite  of 
the  9th  was  not  in  the  place  where  it  was  then  seen. 

On  the  31st  of  January,  1791,  a  satellite  was  observed 
in  opposition  to  the  second,  and  at  about  double  the  dis- 
tance from  the  planet. 

On  the  26th  of  February,  1792,  a  star  toward  the  south, 
at  double  the  distance  of  the  first  satellite,  was  pointed 
out,  but  it  has  not  been  accounted  for  in  succeeding 
observations. 

On  the  5th  of  March,  1796,  Herschel  recorded,  "  I  sus- 
pected a  very  small  star  between  c  and  7i,  which  was  not 
there  last  night.  I  had  a  pretty  certain  glimpse  of  it. 
With  600  I  see  the  satellite  c  better  than  before,  but  can 
not  perceive  the  suspected  small  star." 

On  the  llth  of  February,  1798,  an  exterior  satellite 
was  observed,  and  its  situation  measured. 

There  are  four  instances  in  which  Herschel  observed 
what  he  called  "  the  most  distant  satellite." 

On  the  28th  of  February,  1794,  Herschel  remarked  a 
very  small  star  which  he  did  not  see  on  the  26th. 

On    the    27th   of   March,    1794,    he    obtained   lucid 


ON  THE  SATELLITES  OF  UKANUS.  105 

glimpses  of  some  stars  south,  but  not  one  of  them  could 
lie  see  for  any  constancy. 

On  the  28th  of  March,  1797,  he  observed  an  ex- 
cessively small  star  about  four  times  the  distance  of 
the  second  satellite,  which  he  did  not  remember  to  have 
seen  on  the  25th. 

On  the  16th  of  February,  1798,  a  very  faint  satellite 
was  observed,  and  from  its  distance  was  supposed  to  be  a 
little  before  or  after  its  greatest  southern  elongation.  It 
was  so  faint  that  a  small  alteration  in  the  clearness  of  the 
air  rendered  it  invisible.  On  the  18th  this  satellite  was 
seen  again,  and  being  nearer  the  planet  than  it  was  on  the 
16th,  it  was  supposed  to  be  on  its  return  from  the  greatest 
southern  elongation.  It  was  also  ascertained  on  the  18th 
that  it  had  left  the  place  where  it  was  seen  on  the  16th. 

On  the  strength  of  the  preceding  observations  it  has 
been  generally  admitted  that  Uranus  has  six  satellites; 
but  Mr.  Lassell,  during  his  residence  at  Malta,  carefully 
scrutinized  the  neighborhood  of  the  planet  to  the  distance 
of  five  minutes  from  his  center,  for  the  discovery  of  satel- 
lites. In  the  course  of  this  scrutiny,  he  made  many 
measurements  and  diagrams  of  the  positions  of  small 
points  of  light,  which  all  turned  out  to  be  stars,  and  he 
adds,  "  I  can  not  now  resist  the  conviction,  amounting  in- 
deed in  my  own  mind  to  certainty,  that  Uranus  has  no 
other  satellites  (except  four)  visible  with  my  eye  and  optical 
means.  In  other  words,  I  am  fully  persuaded  that  either 
he  has  no  other  satellites  than  these  four,  or  if  he  has,  they 
remain  yet  to  be  discovered." 

5* 


106 


HISTORY  OF  ASTRONOMY. 


The  following  diagram  represents  the  apparent  orbits 
of  the  four  satellites  of  Uranus  for  November,  1852. 
The  major  axes  of  all  the  orbits  are  nearly  perpendicular 
to  the  ecliptic;  The  minor  axis  of  each  of  the  apparent 
orbits  is  about  three  quarters  of  the  major  axis,  but  the 
true  orbits  of  the  satellites  differ  very  little  from  circles. 


*••-.,. 


\      \ 


1) 


APPARENT  OBBITS  OF  THE  SATELLITES  OF  TJBANUS  FOB  NOVEMBER,  1852. 

The  planet  Uranus  is  fast   approaching  the  position 
most  favorable  for  the  observation  of  its  satellites.     It,  has 


ON  THE  SATELLITES  OF  UKANUS.  107 

now  a  north  declination  of  17  degrees,  which  will  con- 
tinue to  increase  until  1868 ;  and  in  1862,  the  orbits  of 
the  satellites  will  appear  sensibly  circular.  It  is  evident 
then  that  the  period  is  near  at  hand  when  this  planet  can 
be  observed  more  advantageously  than  at  any  former 
time  since  the  first  observations  of  Sir  William  Herschel, 
and  it  is  presumed  that  astronomers  will  not  fail  to  im- 
prove this  opportunity  to  attain  all  the  information 
within  the  reach  of  our  instruments,  both  respecting  the 
physical  peculiarities  of  the  primary,  and  the  number  and 
period  of  its  satellites. 


SECTION    7. 

DISCOYERY  OF  A  NEW  RING  TO  SATURN. 

THE  planet  Saturn  has  long  been  known  to  be  sur- 
rounded by  two  rings.  In  the  year  1610,  Galileo,  with  a 
very  indifferent  telescope,  saw  the  planet  like  a  central 
globe  between  two  smaller  ones.  In  1656,  Huygens  gave 
the  true  explanation  of  these  appearances,  and  showed 
that  the  planet  is  surrounded  by  a  luminous  ring,  in  the 
center  of  which  it  is  suspended.  In  1675,  Cassini  saw 
the  dark  elliptic  line  which  divides  the  ring  into  two 
concentric  portions,  and  he  noted  the  unequal  brilliancy 
of  the  rings,  the  inner  one  being  the  brightest.  Several 
astronomers  have  suspected  the  existence  of  more  than 
two  rings  about  Saturn.  On  the  25th  of  April,  188T, 
Professor  Encke,  at  Berlin,  saw  the  outer  ring  divided  into 
two  nearly  equal  parts,  and  several  divisions  were  recog- 
nized on  the  inner  edge  of  the  inner  ring.  On  the  7th  of 
September,  1843,  Messrs.  Lassell  and  Dawes  saw  what 
they  considered  to  be  a  division  of  the  outer  ring.  The 
division  of  the  outer  ring  has  also  been  noticed  by  Cap- 
tain Kater  in  England,  M.  De  Yico,  at  Rome,  and 
Quetelet,  at  Paris.  The  newly-discovered  ring  of  Saturn 
can  not  be  classed  with  the  subdivisions  of  the  old  ring, 
as  it  Hes  within  its  inner  edge. 


110  HISTOKY  OF  ASTRONOMY. 

The  following  is  the  account  of  the  grand  discovery  of 
a  new  ring  by  the  Messrs.  Bond,  at  Cambridge : 

"November  11,  1850.  We  notice  to-night  with  full 
certainty  the  filling  up  of  light  inside  of  the  inner  ring  at 
x  and  y  (see  drawing  on  page  109).  Also  where  the  ring 
crosses  the  ball  from  c  to  c?,  or  apparently  below  its  pro- 
jection, is  a  dark  band,  no  doubt  the  shadow  of  the  ring 
upon  the  ball ;  but  what  is  very  singular,  there  is  also  a 
dark  line  from  a  to  5,  or  above  the  ring,  very  plainly  seen, 
so  that  there  can  be  no  question  as  to  the  line  where  the 
upper  edge  of  the  ring  crosses  the  ball.  The  light  which 
fills  the  space  at  x  and  y,  is  suddenly  terminated  on  the 
side  toward  the  ball.  It  does  not  arise  from  any  optical 
deception,  for  this  would  give  a  similar  appearance  to  the 
outside  of  the  ring,  or  indeed  to  the  edge  of  any  object 
we  look  at,  which  certainly  is  not  the  case. 

"  November  15,  7h  50m.  The  new  ring  is  sharply  de- 
fined on  the  edge  next  to  the  ball.  W.  0.  Bond  thinks 
he  sees  the  new  ring-  clear  of  connection  with  the  old. 
But  the  side  next  to  the  old  ring  is  not  so  definite  as  that 
next  to  the  planet,  so  that  it  is  not  certain  whether  the 
new  ring  is  connected  with  the  old  or  not.  Where  the 
dusky  ring  crosses  Saturn,  it  appears  a  little  wider  at  the 
outside  of  the  ball  than  in  the  center.  Where  it  crosses 
the  ball,  it  is  not  quite  so  dark  as  the  shadow  of  the 
ring. 

"  8h  p.  M.  Can  not  be  sure  of  a  division  between  the 
new  and  old  rings  (other  than  the  difference  of  light). 
Once  or  twice  with  the  higher  powers,  one  was  suspected. 


DISCOVERY  OF  A  NEW  RING  TO  SATURN.          Ill 

On  further  examination  we  agree  that  the  dark  ring  is 
narrower  than  the  outer  ring.  Its  inner  edge  may  be  as 
far  from  the  inner  edge  of  the  broad  ring  as  two  thirds 
of  the  breadth  of  the  outer  ring." 

The  appearances  above  described  had  been  noticed  on 
many  occasions  prior  to  the  above  dates,  but  their  true 
explanation  was  first  ascertained  on  the  evening  of 
November  15th.  The  fact  of  the  existence  of  a  dusky 
ring  hitherto  unknown  contained  in  the  space  between 
the  old  ring  and  the  ball  could  no  longer  be  questioned. 
Observations  continued  to  the  7th  of  January,  1851,  fully 
confirmed  the  deductions  which  the  Messrs.  Bond  had 
drawn  from  those  of  the  llth  and  15th  of  November. 

Similar  appearances  were  noticed  by  the  Kev.  "W.  B. 
Dawes  at  his  observatory  near  Maidstone  in  England,  on 
the  29th  of  November,  1850.  His  telescope  was  a  re- 
fractor by  Merz  &  Son  of  Munich,  having  an  aperture  of 
six  inches.  He  states  that  on  the  29th  he  observed  a 
shading  like  twilight  at  the  inner  portions  of  the  inner 
ring.  Also  an  exceedingly  narrow  black  line  on  the  ball 
at  the  southern  edge  of  the  ring  where  it  crosses  the 
planet,  and  it  was  slightly  broader  at  the  east  and  west 
edges  of  the  ball  than  near  its  middle.  On  the  3d  of  De- 
cember he  again  saw  the  same  phenomenon,  as  did  also 
Mr.  Lassell  of  Liverpool,  who  was  on  a  visit  to  Mr. 
Dawes's  observatory.  Mr.  Lassell  stated  that  the  space 
between  the  inner  diameter  of  the  inner  ring  and  the  ball, 
was  half  covered  by  an  appearance  as  if  a  crape  vail  had 
been  thrown  over  it.  There  is  a  dark  inner  edge  to  the 


112  HISTORY  OF  ASTRONOMY. 

bright  ring,  which  shades  off  a  little.  The  dark  ring  is 
there  of  a  uniform  gray  color ;  the  sky  is  seen  black  be- 
tween Bond's  ring  and  the  planet. 

An  appearance  somewhat  similar  to  that  described  by 
Mr.  Bond  was  seen  by  Dr.  Galle  at  the  Berlin  observatory 
in  the  years  1838  and  1839.  The  following  are  the 
observations  of  Dr.  Galle : 

"  1838,  May  25th.  The  dark  space  between  Saturn 
and  his  ring  seemed  to  consist,  as  far  as  its  middle,  of  the 
gradual  extension  of  the  inner  edge  of  the  ring  into  the 
darkness,  so  that  the  fading  of  this  inner  ring  has  con- 
siderable breadth. 

"  June  10.  The  inner  edges  of  the  first  ring  fade 
away  gradually  into  the  dark  interval  between  the  ring 
and  the  ball.  It  seemed  that  the  ring,  from  the  begin- 
ning of  the  shading  inclusive,  extends  over  nearly  half 
the  space  toward  the  ball  of  Saturn. 

"  June  15.  The  fading  of  the  inner  ring  toward 
Saturn,  as  on  June  10." 

The  memoir  containing  these  observations  was  pub- 
lished in  the  Transactions  of  the  Berlin  Academy  of 
Sciences  for  1838 ;  it  attracted,  however,  but  little  at- 
tention until  after  the  announcement  of  the  discovery  of 
the  Messrs.  Bond. 

Professor  A.  Secchi,  of  the  observatory  at  Eome,  re- 
marks that  this  species  of  penumbra  in  the  interior  of  the 
ring  of  Saturn  existed  in  the  year  1828,  at  which  time  it 
was  seen  with  the  telescope  of  Cauchoix,  then  recently 


DISCOVERY  OF  A  NEW  RING  TO  SATURN.          113 

received.  The  dark  ring  was  perceived,  although,  its 
nature  was  not  comprehended. 

The  preceding  observations  naturally  suggest  the  in- 
quiry, whether  this  newly-discovered  ring  is  one  of 
recent  formation,  or  has  it  existed  from  time  immemorial  ? 
Sir  William  Herschel  diligently  observed  this  planet; 
yet  only  on  four  occasions  did  he  notice  any  thing  re- 
markable in  the  interior  portion  of  the  ring  beyond 
a  slight  shading  off,  which,  is  represented  in  one  of  his 
figures  of  the  planet,  but  is  not  thought  worthy  of 
particular  description. 

Professor  Struve  remarks  (Memoirs  of  the  Astronomical 
Society,  vol.  2),  "  the  inner  ring  toward  the  planet  seems 
less  distinctly  limited,  and  to  grow  fainter,  so  that  I  am 
inclined  to  think  that  the  inner  edge  is  less  regular  than 
the  others."  Neither  did  Sir  J.  Herschel  at  the  Cape 
of  Good  Hope  notice  any  thing  like  the  present  appear- 
ances, though  Saturn  was  nearly  in  the  zenith,  and  the 
climate  so  favorable. 

In  a  paper  published  in  the  Memoirs  of  the  Academy 
of  Sciences  of  St  Petersburg,  M.  Otto  Struve  attempts  to 
show  that  the  observations  of  various  astronomers  an- 
terior to  the  year  1838,  afford  unequivocal  indications  of 
the  existence  of  the  obscure  ring.  He  remarks  that  the 
early  astronomers  generally  make  mention  of  a  dark  belt, 
(termed  the  equatorial  belt)  which  was  seen  passing 
across  the  body  of  the  planet,  immediately  contiguous  to 
the  inner  edge  of  the  interior  bright  ring.  J.  Cassini 
showed  in  1715  that  from  its  slight  curvature  the  equa- 


HISTORY  OF  ASTRONOMY. 

torial  belt  could  not  be  situate  close  to  the  surface  of  tlie 
planet.  In  1723,  Halley  remarked  that  the  dusky  line 
which  in  1720  he  observed  to  accompany  the  inner  edge 
of  the  ring  across  the  disc,  continued  close  to  the  same, 
though  the  breadth  of  the  ellipse  had  considerably  in- 
creased since  that  time.  M.  Struve  remarks  that  the 
projection  of  the  obscure  ring  upon  the  body  of  the  planet 
agrees  with  the  position  assigned  by  the  earlier  observers 
to  the  equatorial  belt,  and  that  no  trace  of  the  latter  is 
visible  upon  the  planet  in  the  present  day.  He  therefore 
arrives  at  the  conclusion  that  the  obscure  ring  has  ex- 
isted around  the  planetf  at  least  since  the  time  when 
telescopes  were  first  constructed  of  sufficient  optical 
power  to  exhibit  the  belts  upon  his  disc. 

The  breadth  of  the  space  which  separates  the  inner  edge 
of  the  interior  bright  ring  and  the  body  of  the  planet  hav- 
ing exhibited  a  considerable  discordance  as  measured  by 
himself  in  1851,  and  by  his  father  in  1826,  M.  Otto  Struve 
instituted  a  careful  examination  of  the  various  measure- 
ments of  preceding  astronomers  relative  to  the  dimensions 
of  the  planet  and  the  rings.  By  a  comparison  of  the  micro- 
metrical  measures  of  Huygens,  Cassini,  Bradley,  Her- 
schel,  "W.  Struve,  Encke  and  Galle,  with  the  correspond- 
ing measures  executed  by  himself,  he  found  that  the 
inner  edge  of  the  interior  bright  ring  is  gradually  ap- 
proaching the  body  of  the  planet,  while  at  the  same  time 
the  total  breadth  of  the  two  bright  rings  is  constantly 
increasing.  The  earlier  measures  employed  in  this  com- 
parison are,  however,  founded  upon  certain  assumptions 


116  HISTORY  OF  ASTKONOMY. 

relative  to  the  effects  of  irradiation,  and  can  not  there- 
fore be  regarded  as  altogether  trustworthy.  From  a  com- 
parison similar  to  that  instituted  in  the  previous  case,  M. 
Struve  infers,  that  during  the  interval  which  elapsed  be- 
tween the  observations  of  J.  D.  Cassini  and  those  of  Sir 
William  Herschel,  the  breadth  of  the  inner  ring  had 
increased  in  a  more  rapid  ratio  than  that  of  the  outer 
ring.  The  subsequent  measures  seem  to  indicate  a 
reversal  of  this  process. 

By  observations  made  by  Mr.  Lassell  at  Malta  in  1852, 
it  appears  that  the  new  ring  is  transparent  to  such  a 
degree,  that  the  body  of  the  planet  can  be  seen  through 
it.  The  following  is  the  language  of  Mr.  Lassell :  "  Per- 
haps the  most  remarkable  phenomenon  which  I  now 
notice  for  the  first  time  is  the  evident  transparency  of 
the  obscure  ring ;  both  limbs  of  the  planet  being  dis- 
tinctly seen  through  it  where  it  crosses  the  ball,  quite 
through  to  the  edge  of  the  inner  bright  ring.  To  my 
apprehension  I  can  not  better  describe  the  entire  aspect 
of  the  obscure  ring  than  by  comparing  it  to  an  annulus 
of  black  crape  stretched  within  the  bright  ring,  which, 
when  projected  against  the  black  sky,  as  at  the  curve, 
would,  from  its  reflecting  some  light,  appear  of -a  dark 
gray  shade ;  and  when  projected  on  the  ball,  would,  from 
th*  transmission  of  a  portion  of  the  reflected  light  of  the 
ball,  appear  of  a  much  lighter  gray.  What  the  precise 
nature  of  this  marvelous  appendage  can  be  would  be 
an  interesting  subject  of  speculation,  exhibiting  as  it  were 
a  connecting  link  between  nebulous  and  solid  matter. 


DISCOVERY  OF  A  NEW   RING  TO  SATURN.  117 

The  precise  definition  of  its  edges  renders  it  unlike  any 
other  specimen  of  nebulae ;  while  on  the  other  hand  its 
certain  translucencj  deprives  it  of  all  resemblance  to  the 
other  solid  bodies  of  our  system."  The  drawing  on  page 
115  is  copied  from  one  furnished  by  Mr.  Lassell  from  his 
observations  made  at  Malta  in  1852. 

Mr.  Gr.  P.  Bond  maintains  that  Saturn's  ring  is  in  a 
fluid  state,  or  at  least  does  not  cohere  strongly.  The 
following  are  some  of  the  considerations  upon  which  he 
founds  this  conclusion.  Several  observers,  among  whom 
are  Kater,  Encke,  De  Vico,  and  Lassell,  have  seen,  di- 
visions both  of  the  outer  and  inner  ring.  On  the  other 
hand,  some  of  the  best  telescopes  in  the  world,  in  the 
hands  of  Struve,  Bessel,  Sir  John  Herschel,  and  others, 
have  given  no  indication  of  more  than  one  division, 
when  the  planet  has  appeared  under  the  most  perfect 
definition.  The  fact  also  that  the  divisions  on  both  rings 
have  not  usually  been  visible  together,  and  that  the 
telescopes  which  have  shown  distinctly  several  intervals 
in  the  old  ring,  have  failed  to  reveal  the  new  inner  ring, 
while  the  latter  is  now  seen,  but  not  the  former,  indicates 
some  real  alteration  in  the  disposition  of  the  material 
of  the  rings. 

These  facts  are  most  easily  explained  by  supposing 
that  the  rings  are  in  a  fluid  state,  and  within  certain 
limits  change  their  form  and  position  in  obedience  to  the 
laws  of  equilibrium  of  rotating  bodies.  This  hypothesis 
is  favored  by  considerations  drawn  from  the  state  of 
the  forces  acting  on  the  rings.  On  the  assumption  that 


118  HISTORY  OF  ASTRONOMY. 

the  matter,  of  which  the  ring  is  composed,  is  in  a  solid 
state,  we  may  compute  for  any  point  on  its  surface  the 
sum  of  the  attractions  of  the  whole  ring  and  of  Saturn. 
The  centrifugal  force  generated  by  its  rotation,  may  thus 
be  determined  from  the  condition  that  the  particle  must 
remain  on  the  surface.  Now,  in  the  case  of  a  solid  ring, 
particles  on  the  inner  and  outer  edges  must  have  the 
same  period  of  rotation.  This  condition  limits  the 
breadth  of  the  ring ;  for,  if  it  be  found  necessary  for  the 
inner  and  outer  edges  to  have  different  times  of  rotation, 
this  can  be  accomplished  only  by  a  division  of  the  ring 
into  two  or  more  parts.  From  careful  computations,  he 
has  inferred  the  necessity  of  admitting  a  large  number  of 
rings,  provided  they  are  solid.  But  there  are  numerous 
objections  to  admitting  a  large  number  of  small  rings 
near  each  other,  and  to  avoid  these  difficulties,  he  adopts 
the  hypothesis  of  a  fluid  ring.  If  in  its  normal  condition 
the  ring  has  but  one  division,  as  is  commonly  seen, 
under  peculiar  circumstances  it  might  be  anticipated  that 
the  preservation  of  their  equilibrium  would  require  a 
separation  in  some  regions  of  either  the  inner  or  outer 
ring;  this  would  explain  the  fact  of  occasional  sub- 
divisions being  seen.  Their  being  visible  for  but  a  short 
time,  and  then  disappearing,  to  the  most  powerful  tele- 
scope, is  accounted  for  by  the  removal  of  the  sources  of 
disturbance  when  the  parts  thrown  off  would  re-unite. 

Professor  Peirce  has  undertaken  to  show,  from  purely 
mechanical  considerations,  that  Saturn's  ring  can  not  be 


DISCOVERY  OF  A  NEW  RING   ON   SATURN.         119 

solid.  He  maintains  unconditionally  that  there  is  no  con- 
ceivable form  of  irregularity  and  no  combination  of  ir- 
regularities consistent  with  an  actual  ring,  which  would 
serve  to  retain  it  permanently  about  the  primary,  if  it 
were  solid.  He  maintains  that  Laplace's  statement  of  the 
sustaining  power  of  an  irregularity,  was  a  careless  sug- 
gestion, which  was  dropped  at  random,  and  never  sub- 
jected to  the  scrutiny  of  a  rigid  analysis.  Moreover  the 
fluid  ring  can  not  be  regarded  as  one  of  real  permanence 
without  the  aid  of  foreign  support.  This  support  he 
finds  in  the  action  of  the  satellites.  The  satellites  are 
constantly  disturbing  the  ring,  and  yet  they  sustain  it  in 
the  very  act  of  perturbation.  No  planet,  he  thinks,  can 
have  a  ring  unless  it  is  surrounded  by  a  sufficient  number 
of  properly  arranged  satellites. 

"We  might  hope  to  obtain  important  information  re- 
specting the  constitution  of  the  rings  of  Saturn,  if  it  could 
be  observed  in  its  passage  over  some  bright  star.  In  that 
case  the  light  of  the  star  might  be  seen  through  each  suc- 
cessive opening  between  ring  and  ring,  provided  the 
width  of  the  opening  were  sufficient  to  allow  the  visual 
ray  to  clear  the  thickness  of  the  rings.  It  would  be  im- 
portant to  notice  whether  the  light  of  the  star  disappeared 
suddenly  behind  each  of  the  rings  in  succession,  or 
whether  there  was  any  appearance  of  refraction.  Whis- 
ton  informs  us  that  Dr.  Clarke's  father  saw  a  fixed  star 
between  the  ring  and  the  body  of  the  planet ;  and  Pro- 
fessor Kobison  mentions  a  star's  having  been  seen  in  the 


120  HISTORY    OF  ASTRONOMY. 

interval  between  the  two  bright  rings.*  Opportunities 
of  this  kind  are  of  exceedingly  rare  occurrence,  and  it  is 
of  the  highest  importance  that  they  should  always  be  im- 
proved by  nice  micrometrical  measurements. 

*  Smyth's  Celestial  Cycle,  v.  i,  page  193. 


CHAPTER   II. 

RECENT  ADDITIONS  TO  OUR  KNOWLEDGE  OF  COMETS. 


SECTION    I. 

THE  GREAT  COMET  OF  1843. 

MODERN  astronomers  were  generally  agreed  that  the 
ancient  accounts  of  comets  were  greatly  exaggerated; 
for,  said  they,  since  we  have  had  careful  and  scientific 
observers,  the  appalling  comets  of  antiquity  have  dis- 
appeared. What  then  shall  we  say  of  a  comet  in  the 
nineteenth  century,  rivaling  the  noonday  splendor  of  the 
sun? 

On  Tuesday,  the  28th  of  February,  1843,  a  brilliant 
body  resembling  a  comet,  situated  near  the  sun,  was  seen 
in  broad  daylight,  by  numerous  observers  in  various  parts 
of  the  world.  It  was  seen  in  each  of  the  New  England 
States  (except,  perhaps,  Rhode  Island),  in  Delaware,  at 
Halifax,  N.  S.,  in  Mexico,  in  Italy,  and  it  is  said  also  in 
the  East  and  West  Indies.  It  was  seen  in  New  England 
as  early  as  half-past  seven  in  the  morning,  and  continued 
till  after  3  P.  M.,  when  the  sky  became  considerably  ob- 
scured by  clouds  and  haziness.  The  appearance  was  that 

6 


122  HISTOEY  OF  ASTRONOMY. 

of  a  luminous  globular  body  with  a  short  train — the 
whole  taken  together  being  found  by  measurement  about 
one  degree  in  length.  The  head  of  the  comet,  as  ob- 
served by  the  naked  eye,  appeared  circular;  its  light 
equal  to  that  of  the  moon  at  midnight  in  a  clear  sky ; 
and  its  apparent  size  about  one  eighth  the  area  of  the  fall 
moon.  Some  of  the  observers  compared  it  to  a  small 
cloud  strongly  illuminated  by  the  sun.  The  train  was  of 
a  paler  light,  gradually  diverging  from  the  nucleus,  and 
melting  away  into  the  brilliant  sky.  An  observer  at 
Woodstock,  Yt.,  viewed  it  through  a  common  three  fe$t 
telescope.  It  presented  a  distinct  and  most  beautiful  ap- 
pearance— exhibiting  a  very  white  and  bright  nucleus, 
and  a  tail  dividing  near  the  nucleus  into  two  separate 
branches.  At  Portland,  Me.,  Captain  Clark  measured 
the  distance  of  the  nucleus  from  the  sun,  the  only  meas- 
urement (with  one  exception)  known  to  have  been  made 
in  any  part  of  the  globe  before  the  3d  of  March.  At  3h. 
2m.  15s.,  mean  time,  the  distance  of  the  sun's  farthest 
limb  from  the  nearest  limb  of  the  nucleus  was  4°  6'  16". 

In  Mexico,  Lat.  26°  8'  K,  Long.  106°  48'  W.  of  Green- 
wich, the  comet  was  observed  from  nine  in  the  morning 
until  sunset,  by  Mr.  Bowring,  and  the  altitude  of  the 
comet  repeatedly  measured  with  a  sextant.  Professor 
Bianchi,  of  Modena,  in  Italy,  writes  that  on  the  28th  of 
February,  the  comet  was  seen  by  numbers  at  Boulogne, 
Parma  and  Genoa. 

It  is  said  also  that  Captain  Bay,  being  at  Conception, 
in  South  America,  saw  the  comet  on  the  27th  of  Feb- 


THE   GREAT  COMET  OF   1843.  123 

ruary,  east  of  the  sun,  distant  about  one  sixth  of  his  diam- 
eter. 

The  comet  was  seen  at  Pernambuco,  Brazil,  and  in  Yan 
Dieman's  Land,  on  the  1st  of  March.  On  the  second,  it 
•was  seen  in  great  brilliancy  at  St.  Thomas,  and  by  various 
navigators  in  the  equatorial  regions.  On  the  evening  of 
the  3d,  it  was  noticed  at  Key  West,  and  excited  much  at- 
tention. On  the  4th,  it  was  seen  by  a  few  in  the  latitude 
of  New  York,  and  on  Sunday  evening  the  5th,  it  was 
noticed  very  generally.  From  this  date,  until  about  the 
close  of  the  month,  it  presented  a  most  magnificent  spec- 
tacle every  clear  evening  in  the  absence  of  the  moon. 
As  seen  near  the  equator,  the  tail  had  a  darkish  line  from 
its  head  through  the  center  to  the  end.  It  was  occasion- 
ally brilliant  enough  to  throw  a  strong  light  upon  the 
sea.  The  greatest  length  of  tail  was,  about  the  5th  of 
March,  69°  as  measured  with  a  sextant,  and  it  was  ob- 
served to  have  considerable  curvature.  One  observer  de- 
scribes it  as  an  elongated  birch  rod  slightly  curved,  and 
having  a  breadth  of  one  degree.  At  the  Oape  of  Good 
Hope,  on  the  3d,  it  is  described  as  a  double  tail,  about 
25°  in  length,  the  two  streamers  making  with  each  other 
an  angle  of  about  a  quarter  of  a  degree,  and  proceeding 
from  the  head  in  perfectly  straight  lines.  The  greatest 
length  of  tail  observed  in  the  United  States,  was  about 
50°.  The  curvature  of  the  tail  upward,  though  very 
noticeable,  scarcely  exceeded  two  degrees.  The  first  ob- 
servation of  the  nucleus  (with  the  exception  of  the  noon- 
day observations)  is  believed  to  have  been  made  at  the 


THE  GREAT  COMET  OF   1843.  125 

Cape  of  Good  Hope,  on  the  3d,  after  which  it  was  ob- 
served regularly  until  its  disappearance.  At  Trevandran, 
in  India,  it  was  observed  from  the  6th ;  at  Cambridge, 
Mass.,  it  was  observed  on  the  9th,  and  at  numerous  places 
on  the  llth.  The  first  European  observation  of  the  nu- 
cleus was  made  on  the  17th  at  Home  and  Naples,  after 
which  it  was  seen  at  most  of  the  continental  observatories 
till  the  end  of  March. 

The  comet  nowhere  continued  visible  many  days.  It 
was  seldom  seen  in  Europe  after  the  1st  of  April.  The 
last  observation  at  Naples  was  on  the  7th.  Only  one 
later  observation  has  been  announced  from  Europe.  This 
was  at  Berlin,  on  the  15th,  when  Professor  Encke  thought 
he  caught  a  faint  glimpse  of  the  comet,  but  it  could  not 
be  found  again  on  the  subsequent  evening.  The  most 
complete  series  of  observations  in  this  country  was  made 
by  Messrs.  Walker  and  Kendall  of  Philadelphia,  where 
the  comet  was  followed  until  April  10th.  At  Hudson, 
Ohio,  the  comet  was  seen  for  the  last  time  April  6th. 

A  great  many  astronomers  have  computed  the  orbit  of 
this  comet,  and  have  obtained  very  extraordinary  results. 
The  comet  receded  from  the  sun  almost  in  a  straight  line, 
so  that  it  required  careful  observations  to  determine  in 
which  direction  the  comet  passed  round  the  sun,  and  some 
at  first  obtained  a  direct  orbit,  when  it  should  have  been 
retrograde.  The  perihelion  distance  was  extremely  small, 
very  little  exceeding  the  sun's  radius.  Some  have  ob- 
tained a  smaller  quantity  than  this,  but  such  a  supposi- 
tion seems  to  involve  an  impossibility.  It  is  certain, 


126  HISTORY  OF  ASTRONOMY. 

however,  that  the  comet  almost  grazed  the  sun ;  perhaps 
some  portion  of  its  nebulosity  may  have  come  into  direct 
collision  with  it.  The  best  orbits  give  a  perihelion  dis- 
tance of  -0056,  or  a  distance  of  90,000  miles  from  the 
sun's  surface,  which  is  equal  to  about  one  fifth  of  the  sun's 
radius. 

The  velocity  with  which  the  comet  whirled  round  the 
sun  at  the  instant  of  perihelion  was  prodigious.  This 
was  such  as,  if  continued,  would  have  carried  it  round 
the  sun  in  two  hours  and  a  half;  in  fact,  it  did  go  more 
than  half  round  the  sun  in  this  time.  In  one  day  (that 
is  from  twelve  hours  before,  to  twelve  hours  after  peri- 
helion passage),  it  made  291  degrees  of  anomaly;  in 
other  words,  it  made  more  than  three  quarters  of  its 
circuit  round  the  sun.  In  40  days,  the  period  of  its 
visibility,  it  had  described  173  degrees  from  perihelion  ; 
while  to  describe  the  next  seven  degrees  requires  a 
period  of  many  years,  and  perhaps  centuries. 

The  head  of  this  comet  was  exceedingly  small  in  com- 
parison with  its  tail.  "When  first  discovered,  many  were 
unwilling  to  believe  it  a  comet,  because  it  had  no  head. 
The  head  was  probably  nowhere  seen  by  the  naked  eye 
after  the  first  days  of  March.  At  the  close  of  March  the 
head  was  so  faint  as  to  render  observations  somewhat 
difficult  even  with  a  good  telescope,  while  the  tail  might 
still  be  followed  by  the  naked  eye  about  thirty  degrees. 
Bessel  remarked  that  "  this  comet  seemed  to  have  ex- 
hausted its  head  in  the  manufacture  of  its  tail."  It  is 
not,  however,  to  be  hence  inferred,  that  the  tail  was 


THE   GREAT  COMET   OF    1843. 


really  brighter  than  the  head,  only  more  conspicuous 
from  its  greater  size.  A  large  object,  though  faint,  is 
much  more  noticeable  than  a  small  one  of  intenser  light. 
Thus  the  milky-way  is  little  more  than  an  assemblage 
of  faint  stars,  no  one  of  which  singly  would  make  any 
distinct  impression  upon  the  naked  eye. 

The  nearest  approach  of  the  comet's  head  to  the  earth 
was  about  80  millions  of  miles,  being  very  soon  after  the 
perihelion  passage.  The  absolute  diameter  of  the  neb- 
ulosity surrounding  the  head  was  about  36,000  miles. 
The  apparent  length  of  the  tail  has  already  been  stated ; 
but  the  absolute  dimensions  were  still  more  extraordinary. 
.The  following  table  was  computed  from  the  best  ob- 
servations, and  shows  the  progress  of  the  formation  of 
the  tail  after  perihelion.  The  comet  passed  its  perihelion 
on  the  afternoon  of  February  the  27th,  Greenwich 
time. 


Length  of  tall. 
Miles. 


February  28,    35,000,000 


March 


55,000,000 
70,000,000 


3,    82,000,000 


91,000,000 
96,000,000 

6,  99,000,000 

7,  100,000,000 

8,  101,000,000 

9,  102,000,000 
11,  103,000,000 
13,  104,000,000 


March 

u 
u 
a 
u 
u 
II 
u 
.  It 


April 


Length  of  taiL 
Miles. 

15,  105,000,000 

17,  106,000,000 

18,  106,000,000 

19,  107,000,000 

20,  107,000,000 

21,  108,000,000 
24,  108,000,000 
263  106,000,000 
27,  105,000,000 

30,  101,000,000 

31,  98,000,000 
1,  95,000,000 


The  visible  portion  of  the  tail  attained  its  greatest 
length  early  in  March,  remained  nearly  stationary  for 
some  time,  and  during  the  first  week  of  April  suddenly 


128  HISTOEY  OP  ASTKONOMY. 

disappeared,  from  increased  distance,  without  any  great 
diminution  of  length.  The  comet  doubtless  had  a  tail 
before  perihelion,  but  it  seems  physically  impossible  that 
this  should  have  formed  any  part  of  that  which  was  seen 
after  perihelion.  The  tail  was  turned  nearly  toward  the 
earth  on  the  night  of  February  27th,  in  such  a  direction, 
that  had  it  reached  the  earth's  orbit,  it  would  have  passed 
fifteen  millions  of  miles  south  of  us.  Its  length  was, 
however,  at  that  time,  insufficient  to  reach  any  consider- 
able part  of  the  distance  to  the  earth. 

What  gave  the  comet  its  extraordinary  brilliancy  on 
the  28th  of  February  ?  Evidently  its  proximity  to  the 
sun.  The  day  before  it  had  almost  grazed  the  sun's 
disc.  The  heat  it  received,  according  to  the  computa- 
tions of  Sir  John  Herschel,  must  have  been  47,000  times 
that  received  by  the  earth  from  a  vertical  sun.  The 
rays  of  the  sun  united  in  the  focus  of  a  lens  thirty  two 
inches  in  diameter,  and  six  feet  eight  inches  focal  length, 
have  melted  carnelian,  agate  and  rock  crystal.  The  heat 
to  which  the  comet  was  subjected  must  have  exceeded  by 
twenty-five  times  that  in  the  focus  of  such  a  lens.  Such 
a  temperature  would  have  converted  into  vapor  almost 
every  substance  on  the  earth's  surface  ;  and  if  any  thing 
retained  the  solid  form,  it  would  be  in  a  state  of  intense 
ignition.  The  comet  on  the  28th  of  February  was  red 
hot — and  for  some  days  after  its  perihelion,  it  retained  a 
peculiar  fiery  appearance.  In  the  equatorial  regions,  the 
tail  is  described  as  resembling  "  a  stream  of  fire  from  a 
furnace."  The  reason  why  the  tail  was  seen  on  the  28th, 


THE   GKEAT  COMET  OF   1843.  129 

was,  that  it  was  turned  almost  directly  toward  the  earth, 
and  we  therefore  saw  it  in  the  direction  of  its  length. 

Has  this  comet  ever  been  seen  before  ?  In  the  year 
1668  a  comet  appeared  very  similar  to  the  present  one. 
Cassini  saw  the  tail  at  Boulogne,  March  10,  and  sub- 
sequently an  hour  after  sunset;  but  the  head  was 
plunged  in  the  rays  of  the  sun.  The  tail  was  45°  in 
length,  and  extended  almost  horizontally  from  west  to 
south.  It  was  so  brilliant  that  its  image  was  distinctly 
seen  reflected  from  the  sea;  but  this  brightness  lasted 
only  three  days.  The  head  was  small  and  faint,  and 
difficult  to  be  seen.  Professor  Henderson,  of  Edinburg, 
computed  the  orbit  of  this  comet,  and  obtained  a  result 
very  similar  to  the  early  results  with  the  comet  of  1843. 
He  then  assumed  the  elements  of  the  latter  comet,  and 
from  them  computed  the  places  in  1668.  The  results 
accorded  pretty  well  with  the  observations.  Mr.  Peter- 
son has  made  the  comparison  with  corrected  elements, 
and  found  the  accordance  still  better.  On  the  whole, 
it  appears  that  the  comets  of  168"8  and  1843  pursued 
nearly  the  same  path,  and  exhibited  nearly  the  same  ap- 
pearances. 

A  similar  comet  was  seen  in  1689.  It  was  not  seen  in 
Europe,  but  was  observed  at  Pekin,  and  was  most  bril- 
liant in  the  southern  hemisphere,  where  the  tail  attained 
the  length  of  about  68°.  The  head  was  bright,  but  the 
tail  was  paler,  and  had  the  shape  of  a  huge  saber  curved 
at  the  extremity.  The  orbit  of  this  comet  was  computed 

by  Pingre,  and  its  elements  agree  pretty  well  with  those 

6* 


130  HISTOEY  OF  ASTRONOMY.          v^ 

of  the  present  comet,  except  the  inclination,  which  was 
too  great.  Professor  Peirce,  of  Cambridge,  has  re-com- 
puted the  orbit  and  obtained  a  much  better  coincidence. 
In  short,  it  appears  that  the  three  comets  of  1668,  1689, 
and  1843,  all  pursued  nearly  the  same  path,  and  presented 
somewhat  similar  appearences.  What  are  we  to  infer  ? 
Mr.  Walker  inferred  that  these  were  different  appearances 
of  the  same  comet,  with  a  period  of  2l£  years,  the  comet 
having  made  seven  revolutions  from  1689  to  1843.  But 
why  was  it  not  seen  at  either  of  the  intermediate  returns? 
Because  (it  is  said)  the  position  of  the  comet  was  unfavor- 
able for  observation.  From  the  position  of  its  orbit,  the 
comet  will  always  have  considerable  southern  declination, 
which  is  unfavorable  to  its  being  seen  in  the  northern 
hemisphere.  This  answer  is  not  entirely  satisfactory,  as 
it  is  improbable  that  so  prodigious  a  tail  should  pass  un- 
noticed during  six  successive  returns. 

Professor  Schumacher  is  inclined  to  regard  this  comet 
as  identical  only  with  that  of  1668,  giving  it  a  period  of 
175  years.  Professor  Peirce  has  made  a  comparison  of 
all  the  best  observations,  and  his  result  is  that  an  ellipse 
of  short  period  is  inadmissible.  The  observations  may 
all  be  represented  by  a  parabola  within  the  usual  limits 
of  the  errors  of  cometary  observations.  An  ellipse  of 
about  180  years  represents  them  a  little  better.  Profes- 
sor Hubbard,  of  the  Washington  Observatory,  has  re- 
cently undertaken  a  thorough  discussion  of  all  the  ob- 
servations of  this  comet,  and  has  computed  the  effect  due 
to  the  perturbations  of  the  planets.  He  finds  the  most 


THE  GREAT  COMET  OF  1843.          131 

probable  orbit  to  be  an  ellipse  of  over  500  years.  We 
seem,  obliged  then,  entirely  to  reject  any  short  period,  as 
20  or  30  years,  and  there  seems  but  slight  probability 
that  this  comet  is  identical  with  that  of  1668.  It  is  doubt- 
ful whether  the  period  of  this  comet  can  be  certainly  de- 
termined until  it  has  been  again  observed  on  its  return  to 
the  sun. 

The  following  circumstances  invest  the  comet  of  1843 
with  peculiar  interest. 

1.  Its  small  perihelion  distance ;  being  as  small  as  that 
of  any  comet  whose  orbit  has  been  computed,  and  nearly 
as  small  as  is  physically  possible. 

And  2.  Its  prodigious  length  of  tail;  being  equal  to 
that  of  any  comet  hitherto  observed. 


SECTION   II. 

FATE'S    COMET    OF    1843. 

ON  the  22d  of  November,  1843,  a  telescopic  comet  was 
discovered  by  M.  Faye,  of  the  Paris  observatory.  It  had 
a  brilliant  nucleus,  and  a  short  tail  like  a  fan  about  four 
minutes  in  length.  It  was  re-discovered  in  this  country 
on  the  27th  of  December,  by  Mr.  J.  S.  Hubbard,  at  New 
Haven.  The  comet  was  closely  watched  at  the  European 
observatories  during  December  and  January,  and  at  the 
Pulkova  observatory  it  was  followed  until  the  10th  of 
April.  The  orbit  was  first  computed  as  usual  on  the  sup- 
position of  its  being  a  parabola,  but  the  parabolic  elements 
being  found  unsatisfactory,  an  elliptic  orbit  was  comput- 
ed, and  the  period  found  to  be  about  seven  years.  Its 
eccentricity  was  found  to  be  0*55,  thus  forming  a  connect- 
ing link  between  the  asteroids  and  comets.  Hitherto 
there  was  a  well-marked  distinction  between  planets  and 
comets.  The  most  eccentric  of  the  planetary  orbits  is 
that  of  Polymnia  (O337)  or  about  one  third.  The  least 
eccentric  cometary  orbit  hitherto  well  established,  was 
that  of  Biela's  comet,  (0*75),  or  almost  exactly  three  quar- 
ters. Faye's  comet,  with  an  eccentricity  of  one  AaZ/*(O55) 
occupies  an  intermediate  rank,  and  nearly  removes  what 


FAYE'S  COMET  OF  1843. 


133 


had  hitherto  been  regarded  as  one  of  the  most  distinctive 
features  of  comets. 


The  position  of  its  orbit  in  the  heavens  is  very  unstable. 
At  aphelion,  its  distance  from  the  sun  is  five  hundred  and 
sixty  millions  of  miles,  bringing  it  into  close  proximity 
to  the  planet  Jupiter.  Such  a  conjunction  happened  in 
1840,  at  which  time  the  attraction  of  Jupiter  for  the  comet 
was  about  one  tenth  "part  of  the  sun's,  and  must  have  pro- 
duced  a  considerable  alteration  of  its  orbit.  In  1815,  the 
comet  probably  came  still  nearer  to  Jupiter,  by  which  its 
former  orbit  must  have  been  greatly  changed.  The  for- 
mer path  of  this  comet  may,  therefore,  have  been  very 
different  from  that  which  it  pursued  in  1843,  and  M.  Yalz 
expressed  the  opinion  that  this  comet  was  identical  with 
the  famous  comet  of  1770.  The  latter  comet,  at  its  ap- 


134  HISTORY    OF  ASTRONOMY. 

pearance  in  1770,  was  found  to  be  moving  in  an  ellipse, 
whose  period  was  only  five  and  a  half  years,  and  astrono- 
mers were  surprised  that  it  had  never  been  seen  before. 
By  tracing  back  its  motion,  it  was  found  that  at  the  be- 
ginning of  1767,  it  was  very  near  to  Jupiter,  and  the  two 
bodies  remained  in  the  neighborhood  of  each  other  for 
several  months.  Computation,  moreover,  disclosed  the 
fact  that  previous  to  1767,  the  elliptic  orbit  which  it  de- 
scribed corresponded  not  to  five,  but  to  fifty  years  of  re- 
volution round  the  sun.  Again,  in  1779,  according  to 
Lexell's  elements,  it  was  500  times  nearer  to  Jupiter  than 
to  the  sun;  so  that  then,  notwithstanding  the  immense 
size  of  the  sun,  its  attractive  power  on  the  comet  was  not 
the  200th  part  of  that  exerted  by  Jupiter.  It  was  found 
that  on  the  departure  of  this  comet  out  of  the  attraction 
of  Jupiter  in  1779,  its  circuit  could  not  be  performed  in 
less  than  twenty  years.  Thus  the  action  of  Jupiter 
brought  the  comet  of  1770  to  us  in  1767,  and  removed  it 
from  us  in  1779.  Moreover,  at  every  revolution,  the 
comet  of  1770  ought  to  come  into  close  proximity  to 
Jupiter,  and  suffer  enormous  perturbations,  and  M.  Valz 
conjectured  that  the  orbit  of  this  comet  had  been  at'  last 
transformed  into  that  of  the  comet  observed  in  1843.  M. 
Le  Verrier  has  undertaken  a  thorough  investigation  of 
this  question,  and  he  thinks  he  has  demonstrated  that 
the  comet  of  1770  has  nothing  in  common  either  with 
Faye's  comet  of  1843,  or  with  that  discovered  by  De 
Vico  in  1844,  or  any  other  comet  whose  orbit  has  been 
computed. 


FAYE'S  COMET  OF  1843.  135 

M.  Le  Terrier  computed  the  perturbations  of  the 
comet  arising  from  the  attraction  of  the  planets  dur- 
ing the  interval  from  1843  to  1851,  and  predicted  that 
this  body  would  return  to  its  perihelion  on  the  3d  of 
April,  1851. 

The  comet  was  seen  at  the  Cambridge  observatory,  in 
England,  on  the  25th  of  December,  1850,  and  was  .fol- 
lowed until  the  4th  of  March.  It  was  described  as  an 
extremely  faint  object,  so  as  to  be  barely  visible.  The 
positions  assigned  to  it,  scarcely  differed  at  all  from  those 
assigned  in  the  Ephemeris  computed  from  the  elements  of 
Le  Verrier.  The  comet  was  discovered  by  Mr.  Bond,  at 
the  Cambridge  (Mass.)  observatory,  on  the  1st  of  January, 
1851. 

Mr.  Bond  describes  the  comet  as  being  at  that  time  a 
very  faint  object  in  the  twenty-three  feet  refractor,  and  as 
appearing  slightly  elongated  in  the*  direction  of  the  sun. 
The  same  body  was  discovered  at  the  Pulkova  observa- 
tory, on  the  24th  of  January. 

Faye's  comet  is  the  fourth  which  has  been  observed  to 
return  to  the  sun  in  conformity  to  a  prediction.  Halley's 
comet  made  its  first  predicted  return  in  1759 ;  Encke's 
comet  in  1822  ;  and  Biela's  comet  in  1832.  Several  other 
comets  have  been  predicted  to  return,  but  these  predic- 
tions have  not  been  verified  by  observation. 

The  comet  of  Faye  may  be  expected  to  arrive  at  peri- 
helion again  in  .October,  1858. 


SECTION   III. 

DE  YICO'S   COMET  OF   1844. 

ON  the  22d  of  August,  1844,  Father  De  Vico,  di- 
rector of  the  observatory  at  Home,  discovered  a  telescopic 
comet  in  the  constellation  of  the  Whale.  He  imme- 
diately announced  the  discovery  to  Professor  Schumacher, 
of  Altona,  but  his  letter  did  not  arrive  till  the  26th  of 
September.  Meanwhile,  the  comet  had  been  discovered 
independently  by  several  different  observers.  It  was 
seen  by  Professor  Encke  at  Berlin  on  the  5th  of  Sep- 
tember, and  on  the  6th  it  was  seen  at  Hamburg  by  M. 
Melhop,  an  amateur  astronomer.  On  the  10th  of  Sep- 
tember it  was  discovered  by  Mr.  H.  L.  Smith  of  Cleveland, 
Ohio,  who  observed  it  every  day  for  nearly  a  fortnight. 
About  the  third  week  in  September,  it  was  just  dis- 
cernible with  the  naked  eye,  and  with  slight  optical  aid 
had  a  very  beautiful  appearance,  the  nucleus  being 
bright  and  star-like,  and  having  a  tail  about  one  degree  in 
length,  extending  in  a  direction  opposite  to  the  sun. 
At  the  Pulkova  observatory,  the  comet  was  followed  till 
the  31st  of  December. 

It  was  soon  found  by  M.  Faye  and  others,  that  the 
comet  deviated  remarkably  from  a  parabolic  orbit ;  and  it 


DE  vice's  COMET  OF  1844.  137 

was  ascertained  that  the  curve  described  was  an  ellipse 
with  a  periodic  time  of  about  five  and  a  half  years.  Dr. 
Briinnow  (formerly  of  Berlin,  but  now  director  of  the 
observatory  at  Ann  Arbor,  Mich.),  undertook  a  thorough 
investigation  of  all  the  observations,  embracing  a  period 
of  more  than  four  months,  and  took  account  of  all 
the  planets  within  the  orbit  of  Uranus.  He  thus  ob- 
tained an  orbit  which  satisfied  all  the  observations  with 
extreme  precision,  and  indicated  that  the  length  of  the 
comet's  revolution  was  1996.5  days,  or  5.4659  years. 
This  period  (supposing  its  orbit  undisturbed)  would  bring 
the  comet  back  to  perihelion  about  the  20th  of  Feb- 
ruary, 1850 ;  but  it  happened,  very  unfortunately,  that 
when  the  comet  was  near  enough  to  the  earth  to  be 
otherwise  discerned,  it  was  always  lost  in  the  sun's  rays  ; 
the  geocentric  positions  of  the  sun  and  comet  at  perihe- 
lion being  nearly  the  same,  and  continuing  so  for  some 
months,  on  account  of  the  apparent  direct  movement  of 
both  bodies. 

At  the  next  visit,  in  the  summer  of  1855,  it  was  sup- 
posed that  the  comet  would  be  more  favorably  located  in 
the  heavens,  and  astronomers  looked  forward  with  great 
interest  for  its  reappearance.  Dr.  Briinnow  calculated 
that  it  would  be  in  perihelion  on  the  evening  of  August 
6th,  1855.  Only  one  observation  of  this  body  has  been 
reported  from  any  part  of  the  world.  On  the  16th  of  May, 
M.  Hermann  Goldschmidt,  of  Paris,  while  searching  for 
the  comet,  found  a  nebulous  body  whose  right  ascension 
was  21h.  41m.  45s. ;  declination  15°  38'south.  It  was  faint, 


138  HISTORY  OF  ASTROXOMY. 

but  well  seen  with  an  object-glass  of  30  lines  aperture, 
and  a  magnifying  power  of  35.  Its  outline  was  ill  defined, 
of  irregular  form,  and  without  tail. 

The  above  position  does  not  differ  much  from  that 
which  De  Vico's  comet  should  have  occupied  if  it  had 
passed  its  perihelion  about  five  days  later  than  that  com- 
puted by  Dr.  Briinnow,  and  M.  Goldschmidt  concluded 
that  he  had  obtained  an  observation  of  De  Vico's  comet. 
But,  according  to  computation,  the  comet  was  much 
nearer  the  earth  on  the  1st  of  August  than  it  was  in 
May,  and  its  position  in  the  heavens  was  more  favorable 
to  its  visibility,  so  that  if  this  comet  was  really  seen  in 
May,  it  is  difficult  to  understand  why  it  was  not  some- 
where seen  at  a  later  period.  Dr.  Briinnow  is  satisfied 
that  this  supposed  observation  was  a  mistake,  and  that 
De  Yico's  comet  was  no  where  seen  in  1855.  He  ac- 
counts for  this  failure  to  find  the  comet  by  the  faintness 
of  the  object  and  the  uncertainty  of  the  ephemeris,  owing 
to  the  difficulty  of  determining  the  time  of  perhelion 


Messrs.  Laugier  and  Mauvais,  of  Paris,  computed  the 
orbit  of  the  comet  of  1585  from  Tycho's  and  Rothmann's 
observations,  and  obtained  elements  very  similar  to  those 
of  De  Vico's  comet.  They,  therefore,  concluded*  that  the 
comet  of  De  Vico  was  identical  with  the  comet  of  1585, 
and  possibly,  also,  with  those  of  1743,  1766  and  1819. 

M.  Le  Verrier  has  undertaken,  by  a  computation  of  the 
perturbations,  to  decide  whether  this  comet  has  been  ob- 
served at  any  former  return  to  the  sun.  He  concludes 


DE  vice's  COMET  OF  1844.  139 

that  this  comet  can  not  be  identical  with  the  famous 
comet  of  1770,  nor  with  that  of  1585,  nor  with  any  other 
on  record,  unless  that  of  1678.  He  has  shown  that  there 
is  strong  reason  to  believe  that  the  comet  of  De  Yico  is 
identical  with  one  observed  in  1678  by  La  Hire,  and  re- 
corded in  the  Histoire  Celeste  of  Lemonnier.  Dr.  Brun- 
now  has  undertaken  similar  computations,  and  has  arrived 
at  the  same  results  as  Le  Yerrier. 


SECTION  IV. 

BIELA'S    COMET. 

ON  the  27th  of  February,  1826,  M.  Biela,  an  Austrian 
officer,  discovered  a  comet;  and  on  computing  its  ele- 
ments, it  was  found  that  the  same  body  had  been  ob- 
served in  1805  and  in  1772.  It  was  soon  discovered 
that  the  comet  made  its  revolution  round  the  sun  in  a 
period  of  six  years  and  two  thirds.  It  was  of  course  pre- 
dicted that  the  comet  would  return  in  1832.  Computa- 
tion also  disclosed  another  fact,  which  excited  no  little 
alarm.  It  was  predicted  that  on  the  29th  of  October, 
1832,  the  comet  would  cross  the  plane  of  the  ecliptic  at 
a  distance  of  less  than  20,000  miles  from  the  earth's  path. 
Now  the  comet's  radius,  from  observations  in  1805,  had 
been  determined  to  be  greater  than  20,000  miles ;  from 
which  it  followed,  that  a  portion  of  the  earth's  orbit 
would  be  included  within  the  nebulosity  of  the  comet. 
It  was  found,  however,  that  the  earth  would  not  arrive 
at  this  point  of  its  orbit  until  a  full  month  afterward. 
There  was,  therefore,  no  great  danger  of  collision ;  never- 
theless, no  little  alarm  was  experienced  by  those  not  much 
conversant  with  astronomy.  The  comet  returned  at  the 
time  predicted,  and  was  observed  by  Sir  John  Herschel ; 


BIELA'S  COMET. 

but  it  was  extremely  faint,  and  could  only  be  seen  in 
good  telescopes. 

In  1839,  this  comet  must  have  returned  again  to  the 
sun ;  but  its  position  was  most  unfavorable  for  observa- 
tion, and  it  is  not  known  to  have  been  observed  at  all. 

In  1846,  this  comet  returned  to  its  perihelion  under 
circumstances  more  favorable  for  observation.  It  was 
first  seen  at  Eome  on  the  26th  of  November,  1845 ;  at 
Berlin  on  the  28th ;  at  Cambridge,  England,  on  the  1st 
of  December,  and  afterward  at  most  of  the  observatories 
of  Europe.  It  continued  to  be  observed  until  the  27th 
of  April,  1846. 

This  return  of  Biela's  comet  will  always  be  remarkable 
in  its  history  for  an  appearance  quite  new  in  the  annals 
of  modern  astronomy.  When  first  observed  through  the 
five-inch  refractor  at  Yale  College,  December  29th,  it 
was  seen  attended  by  a  faint  nebulous  spot,  estimated  to 
be  rather  more  than  a  minute  of  space  distant  from  its 
brightest  point.  This  surprising  phenomenon  was  first 
publicly  announced  by  Lieut.  Maury  of  the  Washington 
observatory.  On  the  13th  of  January,  Lieut.  Maury  dis- 
covered, that  instead  of  being,  as  usual,  a  single  comet, 
it  apparently  consisted  of  two  comets  moving  through 
space  side  by  side.  Each  body  had  all  the  characteristics 
of  a  telescopic  comet,  being  gradually  condensed  toward 
the  center,  without  any  well-defined  disc;  each  being 
elongated  on  the  side  opposite  the  sun.  For  convenience 
of  description,  we  will  designate  one  of  these  bodies  by 
the  name  of  Biela,  and  the  other  as  his  companion. 


142  HISTORY  OF  ASTRONOMY. 

There  are  three  distinct  circumstances  worthy  of  atten- 
tion— their  relative  magnitude,  intensity  of  light,  and  dis- 
tance from  each  other. 

On  the  13th  of  January,  the  companion  was  estimated 
to  have  one  eighth  the  magnitude  of  Biela;  from  this 
time  it  steadily  increased  until  the  middle  of  February, 
when  it  was  judged  to  be  equal  to  Biela ;  after  which  it 
rapidly  declined,  until  it  disappeared  during  the  month  of 
March. 

Again,  on  the  13th  of  January,  the  light  of  the  com- 
panion was  estimated  to  have  one  fourth  the  intensity  of 
Biela ;  from  which  time  its  light  increased  till  the  middle 
of  February,  when  it  was  judged  to  be  somewhat  brighter 

APPEABANCE  OF  BIELA' 8  COMET. 

March  30, 1846.  Feb.  18, 1846.  Dec.  29, 1845. 


than  Biela ;  after  which  it  rapidly  declined,  and  on  the 
1st  of  March  could  with  difficulty  be  seen,  although  Biela 
remained  quite  conspicuous.  At  the  close  of  March  the 


BIELA'S  COMET.  143 

comet  appeared  single,  and  so  continued  until  the  27th 
of  April,  when  it  entirely  disappeared. 

Also  on  the  13th  of  January,  the  distance  of  the  com- 
panion from  Biela  was  estimated  at  about  two  minutes  of 
space ;  near  the  middle  of  February  it  was  five  minutes ; 
on  the  first  of  March  the  distance  was  ten  minutes ;  and 
at  the  close  of  March  it  was  fifteen  minutes. 

The  preceding  facts  afford  abundant  materials  for  spec- 
ulation. What  was  the  relation  of  these  two  bodies? 
The  appearances,  when  first  noticed,  suggested  the  idea 
that  the  companion  was  a  satellite  to  Biela.  Such  an  idea 
is  now  inadmissible.  It  is  found  that  all  the  observations 
are  very  well  represented  by  supposing  that  each  nucleus 
described  an  independent  ellipse  about  the  sun.  Profes- 
sor Hubbard,  of  the  Washington  observatory,  has  com- 
puted the  orbits,  and  finds  that  all  the  observations  of 
each  nucleus  may  be  represented  by  an  elliptic  orbit  within 
the  probable  limits  of  the  errors  of  such  observations; 
from  which  we  must  conclude  that  the  disturbing  in- 
fluence of  one  nucleus  upon  the  other  must  have  been 
extremely  small,  and  the  observations  do  not  appear  to 
be  'sufficiently  precise  to  render  this  influence  in  any  de- 
gree sensible.  The  following  table  shows  the  distance 
of  one  nucleus  from  the  other,  in  a  straight  line,  expressed 
in  English  miles  according  to  the  elements  of  Professor 
Hubbard : 


Distance. 

1845,  Dec.     1,  117,000  miles, 

1846,  Jan.  20,  198,000       " 

28,  213,000      " 
Feb.    9,  227,000       " 


Distance. 
1846,  Feb.  17,  226,000  miles. 

25,  216,000      " 

March    5,  202,000      " 

21,  170.000      " 


144  HISTORY  OF  ASTRONOMY. 

Thus  it  appears  that  these  two  bodies,  during  the  entire 
period  of  their  visibility,  remained  at  a  distance  from 
each  other  less  than  the  mean  distance  of  the  moon  from 
the  earth;  nevertheless,  the  perturbations  arising  from 
their  mutual  attraction,  did  not  change  their  positions  be- 
yond a  very  small  number  of  seconds  at  the  utmost,  from 
which  we  nlust  infer  that  their  masses  were  excessively 
small. 

Biela's  comet  reappeared  August  25,  1852,  and  con- 
tinued visible  till  the  28th  of  September.  The  changes 
of  relative  brilliancy  of  the  two  comets  were  similar  to 
those  observed  in  1846.  For  convenience  of  distinction 
we  will  call  the  most  southern  comet  A,  and  the  most 
northern  B.  The  comet  A  was  observed  from  August 
25th  to  September  25th.  The  comet  B  was  not  noticed 
until  September  15th  and  was  followed  until  September 
28th.  On  the  15th  of  September,  A  was  fainter  than  B ; 
on  the  19th  A  was  brighter  than  B ;  on  the  20th  both 
comets  had  the  same  brightness ;  while  on  the  23d  and 
25th  A  was  fainter  than  B. 

The  apparent  distance  of  one  comet  from  the  other  dur- 
ing the  whole  time  of  their  visibility  was  about  half  a 
degree.  The  absolute  distances  of  the  comets  from  each 
other  according  to  the  computation  of  Professor  D' Arrest 
were  as  follows : 


Distance. 

1852,  Aug.  27,  1,501,000  miles. 

31,  1,531,000  " 

Sep.     4,  1,559,000  " 

8,  1,582,000  " 

12,  1,601,000  " 


Distance. 

1852,  Sep.  16,  1,616,000  miles. 
20,  1,624,000       " 
24,  1,625,000       " 
28,  1,619,000       « 


145 

Thus  it  appears  that  during  the  entire  period  of  the  ob- 
servations in  1852,  the  distance  of  the  two  bodies  from 
each  other  remained  nearly  constant,  and  this  distance 
was  nearly  seven  times  as  great  as  the  greatest  distance  in 
1846.  A  comparison  of  the  observations  made  in  1852 
with  those  made  in  1846,  might  be  expected  to  determine 
the  orbit  of  each  comet  with  great  precision.  But  here 
an  unexpected  difficulty  presented  itself.  It  seems  im- 
possible to  decide  whether  what  was  known  as  the  pri- 
mary nucleus  in  1846,  is  the  same  with  the  comet  A  or  B 
in  1852 ;  for  all  the  observations  are  about  equally  well 
represented  by  either  hypothesis,  but  there  is  a  slight  dif- 
ference in  favor  of  the  hypothesis  that  the  comet  B  in 
1852  was  the  same  as  what  we  have  called  the  primary 
nucleus  in  1846. 

What  then  is  the  history  of  these  two  bodies  ?  Are 
they  both  new  comets — is  one  a  new  comet  and  the  other 
Biela — or  are  both  of  them  parts  of  Biela  ? 

"We  have  seen  that  the  distance  of  the  two  comets  from 
each  other  in  1852  was  more  than  one  and  a  half  millions 
of  miles,  while  in  1846  it  was  only  about  200,000  miles. 
On  the  1st  of  December,  1845,  the  distance  was  only 
117,000  miles,  and  by  following  both  bodies  backward  we 
find  that  about  the  last  of  September,  1844,  their  distance 
from  each  other  was  only  15,000  miles.  Now  the  radius 
of  the  primary  nucleus  has  been  computed  to  be  20,000 
miles ;  from  which  we  must  conclude  that  the  two  bodies 
were  in  contact  in  September,  1844,  and  each  body  was 
within  a  few  hours'  motion,  of  the  place  where  Biela's 

7 


146  HISTOEY  OF  ASTRONOMY. 

comet  should  be  at  that  time,  from  calculations  based  on 
its  path  when  seen  in  1832.  No  doubt  then  Biela  has 
been  separated  into  two  parts,  and  the  separation  probably 
took  place  in  the  latter  part  of  the  year  1844.  With  re- 
gard to  this  last  conclusion  there  is  perhaps  some  room 
for  question.  The  extraordinary  changes  of  brightness 
which  the  two  nuclei  exhibited  both  in  1846  and  1852 
clearly  indicate  that  the  brightness  of  these  objects  does 
not  depend  merely  upon  their  distance  from  the  earth 
and  sun,  but  upon  other  unknown  causes.  These  causes 
might  have  developed  sufficient  brightness  in  the  com- 
panion, at  its  last  two  returns  to  the  sun,  to  render  it 
visible  to  us ;  while  at  its  former  returns,  on  account  of 
its  unfavorable  position,  the  companion  was  too  faint  to 
be  noticed. 

"What  has  caused  this  separation  of  the  comet  into  two 
portions  ?  Was  it  caused  by  collision  with  some  foreign 
body  ?  Such  a  collision  would  have  materially  changed 
the  figure  of  the  orbit,  and  therefore  we  can  not  suppose 
it  to  have  taken  place  since  the  observation  of  the  comet 
in  1772,  when  it  was  found  to  be  pursuing  nearly  the 
same  path  as  at  present.  It  is  probable  that  in  case  of  an 
encounter  with  some  other  body,  both  bodies  would  have 
moved  on  in  some  new  orbit. 

Was  it  caused  by  an  explosion  arising  from  some  in- 
ternal force  ?  Forces  of  this  kind  we  see  in  operation  in 
our  own  globe,  ejecting  liquid  mountains  from  the  bowels 
of  the  earth.  The  surface  of  our  moon  bears  marks  of 
similar  agency — the  sun  appears  agitated  by  powerful 


BIELA'S  COMET.  147 

forces,  perhaps  the  expansion  of  gaseous  substances.  If 
we  knew  that  Biela's  comet  was  a  solid  body,  we  might 
easily  suppose  it  to  have  been  divided  by  some  force 
similar  to  volcanic  agency.  But  most  of  the  matter  of 
this  body  is  of  the  rarest  kind ;  and  it  may  be  doubted 
whether  any  part  of  it  is  in  a  solid  state. 

Was  this  separation  caused  by  a  repulsive  force  emanat- 
ing from  the  sun  ?  The  phenomena  exhibited  by  Halley's 
comet  at  its  return  to  the  sun  in  1835,  require  us  to  ad- 
mit the  existence  of  repulsive  as  well  as  attractive  forces. 
The  effect  of  the  sun's  repulsion  upon  the  atmosphere  of 
the  comet,  would  be  to  distort  it  from  the  spherical  form, 
which  it  would  assume  under  the  attraction  of  the  nucleus 
alone — to  crowd  the  particles  on  the  side  next  the  sun 
nearer  to  the  nucleus,  and  to  drive  those  on  the  opposite 
side  further  from  it — causing  an  oval  form,  whose  length, 
as  compared  with  its  breadth,  would  be  the  greater,  the 
stronger  the  repulsive  force  is  supposed ;  and  the  repuls- 
ive force  may  be  conceived  to  become  so  great  as  to 
drive  the  remoter  particles  beyond  the  influence  of  the 
nucleus,  and  carry  them  off  into  space.  It  is  necessary, 
in  the  opinion  of  Sir  John  Herschel,  to  suppose  that  the 
tail  is  attracted  by  the  nucleus,  otherwise  they  would  at 
once  part  company.  The  compound  mass  of  the  comet  is 
therefore  urged  toward  the  sun  by  the  difference  of  the 
total  attractive  and  repulsive  forces ;  and  so  long  as  the 
repulsive  power  is  insufficient  to  separate  them,  they  will 
revolve  together  as  one  body,  continually  elongating 
itself  as  it  approaches  the  sun,  and  on  the  position  of 


148  HISTORY  OF  ASTEONOMY. 

whose  longer  axis  the  sun  exercises  a  directive  power,  as 
it  would  on  a  magnet,  if  it  were  itself  magnetic  ;  or  rather 
as  a  positively  electrified  body  would  on  a  non-conduct- 
ing body  of  elongated  form  having  one  end  positively, 
and  the  other  negatively  excited. 

As  a  comet  approaches  the  sun,  a  portion  of  its  matter 
appears  to  be  converted  into  vapor.  In  this  vaporization, 
the  two  electricities  might  be  separated,  the  nucleus  and 
tail  being  in  opposite  electrical  states.  If  now  we  sup- 
pose the  sun  to  be  in  a  permanently  excited  electrical  state, 
we  have  an  explanation  of  the  repulsive  force  which  has 
been  ascribed  to  the  sun.  If  the  repulsive  force  of  the 
sun  upon  the  particles  of  the  tail  should  overcome  the 
attraction  of  the  nucleus,  they  must  be  driven  off  irre- 
coverably. Such  a  separation  could  hardly  be  accom- 
plished without  carrying  off  some  portion  of  the  gravi- 
tating matter ;  and  thus  a  new  comet  would  be  formed, 
as  in  the  case  of  Biela. 

Sir  John  Herschel  mentions  another  mode  in  which 
the  division  of  a  comet  might  be  effected.  The  oscilla- 
tions of  a  fluid  covering  a  central  body  may,  under  cer- 
tain conditions  as  to  the  coercive  power  of  that  central 
mass,  cease  to  continue  of  small  extent,  and  may  increase 
in  magnitude  beyond  any  limit  which  analysis  is  capable 
of  assigning,  even  to  the  extent  of  destroying  the  con- 
tinuity of  the  fluid,  and  separating  it  into  distinct  masses. 
If  such  an  extreme  case  could  ever  occur,  it  must  be  in  a 
comet  like  Biela's,  consisting  of  a  mass  of  vapor  with 


BIELA'S  COMET.  149 

very  little  cohesion,  and  in  which,  the  attractive  power  of 
the  nucleus  is  exceedingly  small. 

Professor  Santini,  by  employing  Plantamour's  elements, 
had  computed  that  this  comet  would  arrive  at  its  peri- 
helion in  1852,  Sept.  28.72,  Berlin  mean  time.  An  error, 
however,  has  been  detected  in  Plantamour's  computations, 
which  being  corrected,  reduces  the  time  of  perihelion 
passage  to  Sept.  25.26.  The  mean  time  of  passage  of  the 
two  nuclei  was  found  to  be  Sept.  23.36  ;  that  is,  the  comet 
reached  its  perihelion  nearly  two  days  earlier  than  the 
time  computed  from  observations  at  the  preceding  return. 
Encke's  comet  exhibits  a  similar  peculiarity,  and  this  fact 
is  accounted  for  by  supposing  that  a  thin  ethereal  me- 
dium pervades  the  planetary  spaces,  sufficiently  dense  to 
produce  some  impression  upon  a  comet,  but  incapable  of 
exercising  any  sensible  influence  on  the  movements  of 
the  planets. 

The  Imperial  Academy  of  Sciences  of  St.  Petersburg, 
has  proposed  the  theory  of  Biela's  comet  as  a  prize  prob- 
lem, the  memoirs  to  be  presented  on  the  1st  of  August, 
1857.  The  Academy  demands  a  rigorous  investigation 
of  the  elements  of  the  orbit  described  by  the  center  of 
gravity  of  the  comet,  founded  on  a  discussion  of  all  the 
observations  from  1772  to  1852. 


SECTION   V. 

MISS    MITCHELL'S    COMET. 

THIS  comet  was  discovered  on  the  1st  of  October, 
1847,  by  Miss  Maria  Mitchell,  of  Nantucket.  As  a  re- 
laxation from  the  severer  toil  of  a  systematic  course  of 
observations,  she  had  employed  the  intervals  through  the 
preceding  year  in  sweeping  for  comets ;  but  her  labors 
had  .hitherto  been  only  rewarded  by  a  familiarity  with 
comet-resembling  nebulae,  which  she  had  constantly  and 
carefully  recorded.  The  instrument  employed  on  these 
occasions  was  a  forty-six  inch  refractor,  with  an  aperture 
of  three  inches,  mounted  on  a  tripod,  and  furnished  with 
a  terrestrial  eye-piece  of  moderate  power.  On  the  even- 
ing of  October  1st,  a  circular  nebulous  body  appeared  in 
the  field  of  the  telescope,  a  few  degrees  above  Polaris. 
There  was  scarcely  a  doubt  of  the  cometary  character 
of  this  object,  inasmuch  as  the  region  which  it  occupied 
had  frequently  been  examined.  Still,  as  the  object  was 
faint,  and  the  weather  uncommonly  clear,  a  possibility 
existed  that  this  too  was  a  nebula  not  before  observed. 
On  the  evening  of  the  2d,  its  change  of  place  was  mani- 
fest. •  No  appearance  of  condensation  of  light  toward  its 
center,  nor  any  indication  of  a  train,  could  be  detected. 


MISS  MITCHELL'S  COMET.  151 

It  is  evident  that  its  apparition,  even  to  the  telescope,  was 
sudden.  Its  first  apparent  motion  was  inconsiderable, 
and  the  region  of  its  discovery  had  been  constantly 
swept  over  by  the  assistant  observer  at  Cambridge,  with 
his  excellent  comet-seeker,  even  as  late  as  the  previous 
evening.  This  idea  is  strengthened  by  the  subsequent 
rapid  increase  of  the  brilliancy  of  the  comet,  and  the 
acceleration  of  its  apparent  motion.  On  the  third,  its 
motion  and  brightness  had  much  increased,  and  there  was 
noticed  a  slight  increase  of  light  toward  its  center.  On 
the  4th,  all  observations  were  prevented  by  the  weather. 
On  the  5th  the  evening  was  delightful.  At  an  early 
period  it  was  evident  that  the  comet  must  pass  over  a 
fixed  star  of  the  fifth  magnitude,  and  preparations  were 
made  to  note  the  beginning  and  the  end  of  the  transit ; 
but  the  border  of  the  comet  proved  too  uncertain  to  rely 
upon.  At  lOh.  54m.,  the  star  appeared  to  be  exactly  in 
the  center  of  the  comet ;  and  during  several  seconds  it 
was  impossible  to  determine,  with  a  power  of  100,  in 
which  direction  was  the  greatest  extent  of  nebulosity.  It 
appeared  in  fact  like  the  nucleus  of  the  comet  shining 
through  it  with  undiminished  brilliancy. 

On  the  6th  the  comet  was  visible  to  the  naked  eye,  and 
continued  to  increase  in  brightness  till  obscured  by  the 
light  of  the  moon.  On  the  9th,  as  seen  at  Cambridge,  it 
exhibited  a  faint  train,  a  degree  and  a  half  in  length,  and 
opposite  to  the  sun. 

This  comet  was  discovered  by  M.  De  Yico,  at  Kome, 
on  the  3d  of  October ;  it  was  discovered  by  Mr.  Dawes, 


152  HISTORY  OF  ASTRONOMY. 

of  England,  on  the  7th ;    and  on  the  llth  it  was  dis- 
covered by  Madame  Kiimker,  of  Hamburg. 

As  there  was  no  doubt  of  Miss  Mitchell's  having  been 
the  first  discoverer  of  this  body,  she  seemed  fairly  entitled 
to  the  gold  medal  offered  by  the  King  of  Denmark  for 
the  first  discovery  of  a  comet.  In  consequence,  however, 
of  her  not  having  complied  strictly  with  the  conditions 
of  giving  immediate  notice  of  the  discovery  by  letter  to 
Professor  Airy,  it  was  for  a  time  doubtful  whether  the 
medal  would  not  be  awarded  to  M.  De  Yico.  A  full 
statement  of  the  circumstances  of  the  discovery  having 
been  made  to  the  King  of  Denmark,  his  majesty  ordered 
a  reference  of  the  case  to  Professor  Schumacher,  who 
reported  in  favor  of  granting  the  medal  to  Miss  Mitchell. 
This  report  was  accepted  by  the  king,  and  the  medal  has 
been  transmitted  accordingly.  This  is  the  first  instance 
in  which  the  gold  medal,  founded  by  the  King  of  Den- 
mark in  1831,  for  the  first  discovery  of  a  comet,  has  been 
awarded  to  an  American,  and  the  first  instance  in  which 
it  has  been  awarded  to  a  lady  in  any  part  of  the  world. 

Miss  Mitchell  has  since  been  provided  with  a  comet- 
seeker  of  a  very  large  aperture,  the  manufacture  of  Mr. 
Fitz  of  New  York,  and  the  public  will  therefore  look  for 
additional  discoveries  from  the  same  quarter. 


SECTION  VI. 

THE  EXPECTED  RETURN  OF  THE  GREAT  COMET  OF  1264. 

ONE  of  the  most  splendid  comets  mentioned  in  his- 
tory is  that  which  made  its  appearance  in  the  middle  of 
the  year  1264.  It  is  recorded  in  terms  of  astonishment 
by  nearly  all  the  historians  of  the  age ;  no  one  then 
living  had  seen  any  to  be  compared  with  it.  It  was  at 
the  height  of  its  splendor  in  the  month  of  August,  and 
during  the  early  part  of  September.  When  the  head  was 
just  visible  above  the  eastern  horizon  in  the  early  morn- 
ing sky,  the  tail  stretched  out  past  the  mid-heaven  toward 
the  west,  or  was  fully  100°  in  length.  Both  Chinese  and 
European  writers  testify  to  its  enormous  magnitude.  In 
China,  the  tail  was  not  only  100°  long,  but  appeared 
curved  in  the  form  of  a  saber.  It  continued  visible  until 
the  beginning  of  October,  historians  generally  agreeing  in 
dating  its  last  appearance  on  the  2d  of  October,  or  on  the 
night  of  the  death  of  Pope  Urban  IY.,  of  which  event  it 
seems  to  have  been  considered  the  precursor.  Kough 
approximations  to  the  elements  of  this  comet  were  at- 
tempted by  Mr.  Dunthorne  in  the  middle  of  the  last 
century,  and  subsequently  by  M.  Pingre,  the  well-known 
French  writer  on  the  history  of  comets. 

In  the  year  1556  another  splendid  comet  made  its  ap- 

7* 


154  HISTORY  OF  ASTRONOMY. 

pearance.  It  was  seen  in  some  places  near  the  end  of 
February,  and  was  equal  in  size  to  half  the  moon.  Its 
beard  was  short,  and  was  unsteady.  It  exhibited  a  move- 
ment like  that  of  a  flame,  or  a  torch  disturbed  by  the 
wind.  The  length-  of  its  tail  was  about  four  degrees ;  its 
color  resembled  that  of  Mars,  but  somewhat  paler.  On 
the  12th  of  March  it  had  reached  a  north  declination  of 
42°,  and  it  moved  over  15°  of  a  great  circle  in  a  day.  It 
was  then  distant  from  the  earth  only  about  seven  millions 
of  miles,  and  showed  considerable  train.  It  continued 
visible  until  the  23d  of  April,  when  it  disappeared  in 
consequence  of  its  proximity  to  the  sun.  Dr.  Halley, 
the  second  astronomer  royal  of  England,  computed  the 
elements  of  this  comet;  but  owing  to  the  imperfect  nature 
of  the  observations,  his  elements  were  not  considered 
very  exact.  Mr.  Dunthorne's  results  for  the  comet  of 
1264  were  so  similar  to  those  which  Halley  had  given 
for  the  comet  of  1556,  that  he  was  immediately  led  to 
conclude  these  two  bodies  to  be  identical,  and  the  period 
being  probably  about  292  years,  he  surmised  that  a  re- 
appearance might  be  expected  about  1848. 

About  twenty  years  later,  M,  Pingre  collected  together 
all  the  accounts  he  could  find  relative  to  the  comet  of 
1264,  and  the  result  of  an  elaborate  investigation  was 
that  the  paths  of  the  comets  of  1264  and  1556  might  be 
represented  with  tolerable  accuracy  by  elements  very 
closely  similar;  and  hence  he  regarded  those  bodies  as 
identical,  and  coincided  with  Mr.  Dunthorne  in  anticipa- 
ting its  re-appearance  about  the  year  1848. 


RETURN  OF  THE  GREAT  COMET  OF   1264.  155 

Between  the  years  1843  and  1847,  Mr.  Hind  of  London 
investigated  the  question  of  identity  anew,  and  he  con- 
cluded that  the  comets  of  1264  and  1556  were  very 
probably  the  same,  and  that  a  return  to  perihelion  might 
be  expected  about  the  middle  of  the  nineteenth  century. 

M.  Bomme,  of  Middleburg,  in  the  Netherlands,  has 
computed  the  effects  that  will  be  produced  on  the  period 
of  the  comet's  return  by  the  united  attraction  of  the 
planets.  With  Dr.  Halley's  elements  it  was  found  that 
at  the  time  the  comet  was  visible  in  1264,  it  was  moving 
in  an  ellipse,  with  a  periodic  time  of  112,469  days,  or 
308  years;  but  perturbations,  owing  to  planetary  at- 
traction, quickened  the  return  of  the  comet  by  no  less 
than  5903  days,  so  that  it  was  in  perihelion  in  April 
1556,  and  at  that  time  the  revolution  corresponding  to 
the  elliptic  arc  described  was  112,943  days.  Starting 
again  from  this  epoch,  M.  Bomme  ascertained  that  the 
next  revolution  should  occupy  111,146  days,  bringing 
the  comet  to  its  perihelion  on  the  22d  of  August,  1860,  at 
which  time  the  revolution  will  be  113,556  days. 

Employing  Mr.  Hind's  elements,  it  was  found  that  in 
1264  the  ellipse  described  by  the  comet  had  a  period  of 
110,644  days,  or  302.922  years,  and  that  planetary  dis- 
turbances expedited  its  return  by  4077  days.  At  the  time 
it  was  visible  in  1556,  its  mean  motion  corresponded  to 
a  period  of  308.169  years.  The  present  revolution 
should  be  shortened  by  perturbations  3828  days,  or 
10.48  years,  and  the  comet  should  again  reach  its  peri- 
helion on  the  2d  of  August,  1858,  the  revolution  belong- 


156  HISTOEY   OF  ASTKONOMY. 

ing  to  the  major  axis  at  that  epoch  being  308.784 
years. 

Hence  it  appears  that  there  is  an  uncertainty  of  two 
years  (between  August  1858  and  August  1860)  in  the 
time  of  the  next  arrival  at  perihelion,  according  as  the 
elements  of  Dr.  Halley  or  those  of  Mr.  Hind  are  em- 
ployed. 

It  is  an  important  circumstance  as  bearing  on  the 
question  of  identity  of  the  comets  of  1264  and  1556, 
that  about  289  years  before  the  former  epoch,  or  A.D. 
975,  a  comet  of  great  apparent  magnitude  was  visible, 
which  may  possibly  have  been  the  same.  It  exhibited  a 
tail  40°  in  length.  Assuming  the  elements  obtained  by 
Mr.  Hind  for  the  comet  of  1556,  and  that  the  perihelion 
passage  took  place  early  in  August  975,  it  is  found  that 
the  observed  track  may  be  very  closely  represented. 

It  is,  therefore,  inferred  that  the  next  perihelion  pas- 
sage of  the  comet  of  1264  will  take  place  within  two 
years  of  August  1858 ;  nearer  than  this  it  does  not  ap- 
pear possible  to  approximate  in  the  present  state  of  our 
knowledge. 


SECTION   VII. 

THE  GREAT   COMET  OP   1863. 

THE  great  comet  of  1853  was  discovered  by  M.  Klin- 
kerfues  at  Gottingen  on  the  10th  of  June,  at  which  time 
it  was  a  somewhat  faint  telescopic  object.  About  the 
7th  of  August  it  began  to  be  faintly  visible  to  the  naked 
eye ;  on  the  20th  it  was  equal  to  a  star  of  the  third  or 
fourth  magnitude ;  on  the  25th  it  was  equal  to  a  star  of 
the  second  magnitude ;  on  the  30th  it  was  as  bright  as 
one  of  the  brightest  stars  of  the  first  magnitude.  From 
the  30th  of  August  to  the  4th  of  September,  although 
the  comet  was  distant  but  a  few  degrees  from  the  sun's 
place,  it  was  seen  and  well  observed  each  day  in  full  day- 
light by  M.  Schmidt  of  Olmutz.  On  the  31st  of  August 
he  made  a  series  of  observations  of  the  comet's  place 
with  his  telescope  about  mid-day,  although  the  comet 
was  only  twelve  degrees  from  the  sun ;  and  on  the  2d, 
3d  and  4th  of  September,  he  observed  it  at  mid-day, 
although  only  seven  or  eight  degrees  from  the  sun.  Also 
on  the  3d  of  September,  about  noon,  Mr.  Hartnup,  of  the 
Liverpool  observatory,  saw  the  comet  distinctly  with  his 
telescope. 

For  a  month  after  the  discovery  of  this  comet,  it  ex- 


158  HISTOEY  OF  ASTEONOMY. 

hibited  an  oval  form,  its  greatest,  diameter  being  about 
three  minutes.  After  this  date  it  became  more  elon- 
gated, and  by  the  first  of  August  had  attained  a  length 
of  ten  or  fifteen  minutes.  On  the  20th  of  August  it  ex- 
hibited a  tail  about  one  degree  in  length ;  and  during  the 
next  ten  days  the  tail  rapidly  increased,  attaining  at  last 
a  length  of  about  fifteen  degrees. 

The  comet  passed  its  perihelion  on  the  1st  of  Septem- 
ber ;  and  it  is  not  known  to  have  been  seen  any  where 
in  the  northern  hemisphere  after  the  4th  of  September. 
On  the  16th  of  September  the  comet  was  noticed  at 
Santiago  de  Chili,  and  was  observed  there  till  the  7th  of 
October.  It  was  visible  to  the  naked  eye,  its  nucleus 
being  very  well  defined  ;  but  its  tail  was  so  faint,  that  it 
was  scarcely  possible  to  determine  its  length.  At  the 
Cape  of  Grood  Hope  the  comet  was  seen  and  carefully 
observed  from  the  llth  of  September  until  the  llth  of 
January,  1854.  It  was  also  observed  at  New  Zealand 
from  the  14th  of  September  to  the  10th  of  October.  On 
the  15th  of  September  the  length  of  its  tail  was  about 
five  degrees,  from  which  time  its  brightness  daily 
diminished. 

All  the  observations  of  this  comet  are  tolerably  well 
represented  by  a  parabolic  orbit. 


CHAPTER   III. 

ADDITIONS  TO  OUR  KNOWLEDGE  OF  THE  FIXED  STARS 
AND  NEBULJG. 


SECTION   I. 

DETERMINATION  OF  THE  PARALLAX  OF  FIXED  STARS. 

UNTIL  recently,  astronomers  had  been  unable  to  meas- 
ure the  distance  of  a  single  fixed  star.  The  parallax 
•arising  from  the  motion  of  the  earth  in  its  orbit,  even  for 
the  nearest  fixed  star  which  had  been  examined,  remained 
concealed  among  the  small  errors  to  which  all  astronomical 
observations  are  liable.  Nevertheless,  it  was  generally 
agreed  among  astronomers  that  no  star  visible  in  north- 
ern latitudes,  to  which  attention  had  been  directed,  mani- 
fested an  amount  of  parallax  exceeding  a  single  second  of 
arc.  An  annual  parallax  of  one  second  implies  a  distance 
of  about  twenty  millions  of  millions  of  miles,  a  distance  which 
light,  traveling  at  the  rate  of  192,000  miles  per  second, 
requires  3£  years  to  traverse.  This  being  the  inferior  limit 
which  the  nearest  stars  exceed,  it  is  not  unreasonable  to 
suppose  that  among  the  innumerable  stars  which  the 


160  HISTORY  OF  ASTRONOMY. 

telescope  discloses,  there  may  be  those  whose  light  re- 
quires hundreds,  and  perhaps  thousands  of  years  to  travel 
down  to  us. 

The  difficulty  of  measuring,  by  direct  meridional  ob- 
servations, a  quantity  so  minute  as  the  parallax  of  the 
stars,  has  led  astronomers  to  try  a  system  of  differential 
observations,  susceptible  of  far  greater  accuracy.  Suppose 
there  are  two  stars  at  unequal  distances  from  us,  so  situat- 
ed as  to  appear  nearly  on  the  same  line  of  vision.  Their 
apparent  places  must  be  alike  affected  by  aberration,  pre- 
cession, nutation,  refraction  and  instrumental  errors;  so 
that  although  it  is  difficult  to  determine  the  true  right 
ascension  and  declination  of  either  star  within  one  second 
of  arc,  we  may  measure  the  difference  of  position  of  one 
star  from  the  other  with  extreme  precision,  without  the 
necessity  of  taking  account  of  the  preceding  corrections. 
Now  the  difference  of  position  of  the  two  stars,  if  meas- 
ured for  every  season  of  the  year,  gives  us  their  difference 
of  parallax;  and  if  one  star  is  several  times  more  distant 
than  the  other,  this  difference  of  parallax  will  be  sensibly 
the  entire  parallax  of  the  nearer  star,  This  method  was 
first  proposed  by  Galileo  more  than  two  centuries  ago, 
but  it  does  not  appear  that  he  ever  attempted  to  reduce  it 
to  practice.  Sir  William  Herschel  attempted  to  reduce 
this  method  to  practice,  and  for  this  purpose  he  selected  a 
great  number  of  double  stars  which  in  consequence  of  the 
inequality  of  the  component  members,  appeared  to  be  well 
adapted  to  this  object.  His  labors  led  to  the  discovery 
of  a  physical  connection  between  the  bodies  composing 


THE  PARALLAX  OF   FIXED  STARS.  161 

double  stars,  but  he  did  not  succeed  in  establishing  any 
parallax. 

In  the  year  1837,  the  late  Professor  Bessel  applied  this 
method  to  determine  the  parallax  of  the  double  star  61 
Cygni.  This  is  a  small  star,  hardly  exceeding  the  sixth 
magnitude,  which  had  been  pointed  out  for  special  ob- 
servation by  the  circumstance  of  its  having  a  very  large 
proper  motion,  viz.,  more  than  five  seconds  per  year,  be- 
ing a  more  rapid  motion  than  had  been  detected  (until 
recently)  in  the  case  of  any  other  star,  on  which  account 
it  had  been  suspected  to  be  comparatively  near  our  sys- 
tem. Bessel  repeatedly  measured  the  distance  of  this  star 
from  two  other  stars  in  its  neighborhood,  both  of  them 
very  minute,  and  therefore  presumed  to  be  very  distant : 
and  he  continued  his  observations  every  month,  when 
practicable,  for  three  years.  The  distances  were  measured 
by  means  of  a  magnificent  heliometer,  which  Fraunhofer 
of  Munich,  had  recently  executed  for  the  observatory  of 
Konigsberg.  It  appeared  that  in  January  of  each  year, 
the  distance  of  61  Cygni  from  one  of  the  stars  of  compar- 
ison was  one  third  of  a  second  less  than  the  mean  dis- 
tance ;  while  in  June  it  was  one  third  of  a  second  greater 
than  the  mean.  This  effect  is  precisely  such  as  should  be 
produced  by  the  motion  of  the  earth  about  the  sun,  caus- 
ing an  apparent  displacement  of  the  nearer  stars  as  com- 
pared with  those  which  are  more  remote,  and  as  no  other 
explanation  of  the  phenomenon  seems  admissible,  these  ob- 
servations are  considered  as  settling  the  long  vexed  ques- 
tion of  parallax.  In  1841,  Professor  Bessel  received  the 


162     .  HISTOKY  OF  ASTRONOMY. 

gold  medal  of  the  Koyal  Astronomical  Society  of  Lon- 
don, for  this  important  discovery.  The  parallax  of  61 
Cygni,  according  to  these  observations,  is  0".348,  making 
the  distance  of  this  star  from  the  sun  592,000  times  the 
radius  of  the  earth's  orbit — a  distance  which  light  would 
require  more  than  nine  years  to  traverse. 

This  result  has  received  confirmation  from  the  re- 
searches of  M.  Peters,  who  from  a  series  of  zenith  dis- 
tances of  the  star,  determined  at  the  observatory  of  Pul- 
kova  during  the  years  1842  and  1843,  has  found  its  paral- 
lax to  be  equal  to  0".347.  These  observations  were  made 
with  the  grand  vertical  circle  of  Ertel,  which  is  43  inches 
in  diameter,  graduated  to  2  minutes,  and  reading  by  four 
microscopes  to  one  tenth  of  a  second. 

A  series  of  observations  of  61  Cygni  have  also  been 
made  by  Mr.  Johnson,  with  the  new  heliometer  of  the 
Oxford  observatory.  These  observations  were  com- 
menced in  1852  and  were  continued  through  the  years 
1853  and  1854,  and  they  fully  confirm  the  fact  of  an 
annual  parallax,  very  nearly  of  the  same  amount  as  that 
found  by  Bessel.  The  stars  selected  for  comparison  were 
different  from  those  which  Bessel  used,  both  stars  lying 
nearly  in  the  direction  of  the  components  of  61  Cygni. 
These  observations  give  the  parallax  0".392  or  0".402, 
according  as  a  temperature  correction  is  applied  or  not. 

M.  Otto  Struve,  of  the  Pulkova  observatory,  has  made 
some  observations  of  61  Cygni  with  a  wire  micrometer 
attached  to  his  telescope,  and  a  preliminary  calculation 
has  furnished  for  the  parallax  0".52,  a  result  sensibly 


THE  PARALLAX  OF  FIXED  STARS.        163 

greater  than  has  been  obtained  by  either  of  the  preceding 
observers. 

In  1839,  Professor  Henderson,  of  Edinburgh,  an- 
nounced that  in  discussing  his  observations  of  Alpha 
Centauri  made  at  the  Cape  of  Good  Hope,  with  a  mural 
circle,  during  the  years  1832-3,  he  had  found  evidence  of 
a  sensible  parallax.  The  double  star,  a  Centauri  is  one  of 
the  brightest  stars  of  the  southern  hemisphere.  The  two 
stars  a1  and  a2  are  situated  within  19"  of  space  of  each 
other.  On  comparing  the  observations  of  Lacaille  with 
those  of  the  present  time,  it  is  found  that  although  the 
two  stars  have  not  sensibly  changed  their  relative  posi- 
tions, each  has  an  annual  proper  motion  of  3.6  seconds 
of  space.  It  thus  appears  that  they  form  a  binary  system, 
having  one  of  the  greatest  proper  motions  that  has  been 
observed ;  and  from  this  circumstance,  as  well  as  the 
brightness  of  the  stars,  it  is  reasonable  to  suppose  that 
their  parallax  may  be  sensible.  Professor  Henderson's 
observations  were  not  made  for  the  purpose  of  ascertain- 
ing the  parallax,  but  of  accurately  determining  the  mean 
places  of  the  stars..  On  reducing  the  declinations,  he 
found  a  sensible  parallax,  but  he  delayed  communicating 
the  result  until  it  should  be  seen  whether  it  was  confirmed 
by  the  observations  of  right  ascension  made  by  Lieutenant 
Meadows  with  the  transit  instrument.  These  observa- 
tions also  indicated  a  sensible  parallax.  A  combination 
of  all  Professor  Henderson's  observations  gave  a  parallax 
of  T.16,  with  a  probable  error  of  O'.ll. 

In  1839  and  1840  a  series  of  observations  was  made  by 


164  HISTORY  OF  ASTRONOMY. 

Mr.  Maclear,  at  the  Cape  of  Good  Hope,  for  the  purpose 
of  ascertaining  the  parallax  of  this  star.  The  observations 
consisted  of  double  altitudes  measured  with  the  mural 
circles,  and  they  gave  a  parallax  of  0".91 ;  and  from  sub- 
sequent observations  extending  down  to  1848,  he  found 
it  to  be  0".98. 

Mr.  Maclear  also  made  a  series  of  observations  of  ft 
Centauri,  in  the  years  1842-44,  from  which  he  has  de- 
duced a  parallax  for  this  star  amounting  to  0".47,  with  a 
probable  error  of  0".04. 

In  the  year  1835,  M.  Struve  commenced  a  series  of  ob- 
servations, with  a  view  of  detecting  the  parallax  of  the 
bright  star  a  Lyrse.  His  method  of  observation  consisted 
in  measuring  with  a  micrometer  the  distance  between  this 
star  and  another  very  small  star  situated  about  43"  from 
it,  repeating  the  operation  at  different  seasons  throughout 
the  year.  The  result  of  this  inquiry  assigned  a  parallax 
of  0".26  toaLyrae. 

The  more  recent  researches  of  M.  Peters  at  the  Pul- 
kova  observatory  tend  to  prove  that  this  star  has  a  visible 
parallax,  although  the  result  is  less  than  that  assigned 
by  M.  Struve.  These  observations  were  made  with  the 
great  vertical  circle  of  Ertel,  and  his  result  was  a 
parallax  of  0".10,  with  a  probable  error  of  0".05. 

M.  Otto  Struve  has  recently  given  the  result  of  fifteen 
months'  observations  on  this  star,  and  finds  a  parallax 
of  0//.14.  Combining  this  result  with  the  former  values 
of  M.  Struve  and  Peters,  he  obtains  a  mean  value  of 
0".15,  with  a  probable  error  of  0".01. 


THE  PARALLAX  OF  FIXED  STARS.        165 

The  star  1830  of  Groombridge's  catalogue  (right  as- 
cension llh.  44m.  18s.,  declination  38°  48'  north),  has  the 
largest  proper  motion  at  present  known,  exceeding  7ff  in 
arc ;  and  in  .consequence  various  attempts  have  been  made 
at  different  places  to  determine  its  parallax,  the  prob- 
ability being  great  that  its  parallax  would  be  appre- 
ciable. The  discovery  of  the  proper  motion  was  pub- 
lished by  Argelander  in  the  year  1842,  and  Bessel  was 
induced  to  give  immediate  directions  to  Schliiter,  his 
assistant,  to  commence  a  series  of  measures  with  the 
Konigsberg  heliometer.  These  measures  were  begun  in 
October,  1842,  and  were  terminated  abruptly  near  the  end 
of  August,  1843,  by  the  illness  and  subsequent  death  of 
Schliiter.  M.  Wichmann  was  then  charged  with  the  con- 
tinuation of  the  observations,  but  more  pressing  duties 
prevented  him  from  completing  the  observations  till  the 
year  1851. 

In  the  year  1846  Mr.  Faye,  by  observing  with  the 
equatorial  of  the  Paris  observatory  the  difference  of  right 
ascension  between  this  star  and  that  of  another  small  star 
situated  nearly  on  the  same  parallel,  determined  the 
parallax  to  be  1".08,  and  by  this  striking  result  drew  the 
attention  of  others  to  the  star.  Peters,  by  discussion  of 
his  observations  made  at  Pulkova  with.  Ertel's  circ]er 
subsequently  determined  its  parallax  to  be  0".226,  with  a 
probable  error  of  OM41.  This  result  is  derived  from  48 
zenith  distances  observed  in  1842  and  1843.  Mr.  Wich- 
mann's  discussion  of  Schliiter's  observations  gave  a  parallax 
of  OM8.  M.  Otto  Struve,  by  micrometer  measures  of 


166  ^STOBY  OF  ASTRONOMY. 

differences  of  north  polar  distance  made  with,  the  great 
refractor  in  1848  and  1849,  found  the  parallax  to  be  0".03. 

In  the  yeUr  1852  Mr.  Wichmann  published  the  results 
of  his  new  series  of  observations  with,  the  heliometer 
made  in  1851.  In  these  observations  he  measured  the 
distance  between  1830  Groombridge  and  a  small  star  a 
preceding  by  34'  in  right  ascension,  a  second  star  a'  fol- 
lowing it  by  34'  in  right  ascension,  and  a  third  star  a"  fol- 
lowing it  by  30'  in  right  ascension.  The  result  of  his 
discussion  of  the  observations  was  that  the  parallaxes  of 
the  stars  a'  and  a"  were  of  very  small  amount,  but  that  the 
parallax  of  1830  Groombridge,  amounted  to  0".71,  and 
that  of  the  star  a  to  1".17. 

M.  Peters  has  subjected  the  observations  of  M.  Wich- 
mann to  a  critical  discussion,  and  has  shown  that  "Wich- 
mann's  adopted  temperature  correction  is  probably  too 
small.  He  considers  the  most  trustworthy  result  de- 
ducible  from  the  observations  to  be  a  parallax  of  0".148 
for  1830  Groombridge. 

During  the  years  1852,  '53  and  '54,  a  long  series  of  ob- 
servations of  this  star  were  made  by  Mr.  Johnson  with 
the  Oxford  heliometer,  and  these  also  present  an  anom- 
alous result,  inasmuch  as  they  assign  a  greater  parallax 
to  one  of  the  stars  of  comparison  than  to  1830  Groom- 
bridge  ;  and  what  adds  to  the  perplexity  is,  that  the  star 
which  appears  to  have  the  greater  parallax  in  this  case, 
is  one  of  those  which,  in  M.  "Wichmann's  researches 
appeared  to  be  most  distant.  Mr.  Johnson's  results  are 
a  parallax  of  0".26  for  1830  Groombridge,  and  of  0".44 


THE  PARALLAX  OF  FIXED  STABS.        167 

for  the  star  of  comparison  a\  while  the  parallax  of  star 
a  was  considered  to  be  insensible.  These  results  appear 
to  indicate  some  imperfection  in  double-image  measures 
of  objects  separated  by  large  arcs,  which  still  remains  to 
be  explained. 

Mr.  Henderson  has  attempted  to  determine  the  par- 
allax of  Sirius  from  the  observations  made  with  the 
mural  circle  at  the  Cape  of  Good  Hope  in  the  years  1832 
and  1833,  as  'also  in  1836  and  1837,  being  in  all  231  ob- 
servations. From  these  he  has  deduced  a  parallax  of 
(T.23.  The  error  of  this  determination  he  estimates  not 
to  exceed  a  quarter  of  a  second,  from  which  he  concludes 
that  the  parallax  of  Sirius  is  not  greater  than  half  a 
second  of  space,  and  that  it  is  probably  much  less. 

Numerous  attempts  have  been  made  to  determine  the 
parallax  of  the  pole-star.  From  a  comparison  of  603 
right  ascensions  of  the  pole-star  observed  by  M.  Struve 
and  Preuss  at  Dorpat  from  1822  to  1838,  M.  Peters  has 
deduced  a  parallax  of  OM7,  with  a  probable  error 
of  0".03.  From  a  comparison  of  the  declinations  of  the 
pole-star  observed  at  Dorpat  from  1822  to  1838,  M. 
Peters  has  deduced  a  parallax  of  0".15;  and  by  com- 
paring the  right  ascensions  observed  at  Dorpat  from  1818 
to  1821,  he  has  deduced  the  parallax  of  0*.07.  M.  De 
Lindenau,  from  a  comparison  of  890  right  ascensions  of 
the  pole-star,  observed  by  different  astronomers,  deduced 
a  parallax  of  OM4,  with  a  probable  error  of  0".06.  From 
289  observations  of  the  pole-star  made  at  Pulkova  in  1842 
and  1843  with  the  grand  vertical  circle  of  Ertel,  M.  Peters 


168  HISTORY  OF  ASTRONOMY. 

has  deduced  a  parallax  of  0".07.  Taking  the  mean  of 
all  these  determinations,  M.  Peters  has  obtained  as  a  final 
result  the  parallax  of  the  pole-star  0".106,  or  about  one 
tenth  of  a  second,  a  distance  which  light  would  require 
30  years  to  traverse.  According  to  this  result  it  must 
have  been  30  years  after  the  pole-star  was  placed  in  the 
firmament  before  its  light  shone  upon  the  earth  ;  and  if  it 
were  now  annihilated,  it  would  still  shine  for  30  years 
longer  to  guide  the  mariner  across  the  ocean. 

M.  O.  Struve  has  recently  announced  that  he  has  found 
the  parallax  of  a  Cassiopeae  to  be  0".34  with  a  probable 
error  of  0".05  ;  and  the  parallax  of  a  Aurigae  to  be  0".30 
with  a  probable  error  of  0".04. 

M.  Peters  has  also  attempted  to  determine  the  average 
value  of  the  parallax  of  stars  of  the  different  magnitudes. 
For  this  purpose,  he  availed  himself  of  the  long  series  of 
observations  made  at  Dorpat,  and  concludes  that  the 
average  parallax  of  stars  of  the  second  magnitude  is 
0".116.  Combining  this  result  with  the  relative  distances 
of  stars  of  the  different  orders  as  determined  by  M. 
Struve,  we  are  enabled  to  estimate  the  parallaxes  of  the 
stars  of  the  various  orders,  and  hence  their  absolute  dis- 
tances. The  following  is  M.  Peters'  result  for  stars  of 
the  first  six  magnitudes : 

App.  mag-  paranax<  Distance  in  radii  of      Time  required  for  light  to 

nitude.  the  earth's  orbit.  traverse  this  distance. 

1  0".209                  986,000  15  years. 

2  0".116                1,778,000  28       " 

3  0".076               2,725,000  43       " 

4  0".054                3,850,000  61       " 
6  0".037                5,378,000  85       " 
6  0".027                7616,000  120       " 


THE  PARALLAX  OF  FIXED  STARS.        169 

Thus  light,  which  travels  at  the  rate  of  190,000  miles 
every  second,  requires  15  years  to  come  to  us  from  stars 
of  the  first  magnitude,  and  120  years  to  come  from  one 
of  those  small  stars  which  are  just  visible  to  the  naked 
eye.  These  results  can,  of  course,  only  be  regarded  as 
provisional,  until  sufficient  observations  are  collected  for 
a  more  thorough  investigation  of  the  subject ;  but  it  is 
not  too  much  to  expect  that  ere  long  a  similar  table  for  at 
least  the  brighter  stars  may  be  constructed,  founded  on 
unquestionable  data. 


SECTION   II. 

OBSERVATIONS  OP  NEW  AND  VARIABLE  STARS. 

IT  lias  long  been  known  that  among  the  fixed  stars  are 
several  which  experience  a  periodical  increase  and  dimi- 
nution of  brightness.  The  star  Omicron,  in  the  constella- 
tion Cetus,  sometimes  appears  as  a  star  of  the  second 
magnitude,  but  continues  of  this  brightness  only  about  a 
fortnight,  when  it  decreases  for  about  three  months,  till 
it  becomes  completely  invisible  to  the  naked  eye,  in 
which  state  it  remains  about  five  months,  and  then  in- 
creases again  to  the  second  magnitude,  the  interval  be- 
tween its  periods  of  greatest  brightness  being  about  eleven 
months.  The  star  Algol  varies  from  the  second  to  the 
fourth  magnitude,  going  through  its  changes  in  less  than 
three  days.  More  than  forty  such  cases  have  been  no- 
ticed, although  in  many  of  them  the  change  of  brightness 
is  not  very  remarkable. 

In  the  case  of  a  few  stars,  remarkable  changes  of 
brightness  have  been  observed,  which  have  not  been  re- 
duced to  any  law  of  periodicity.  The  star  t\  (eta)  Argus 
is  of  this  kind.  This  is  a  star  of  the  southern  hemisphere 
in  right  ascension  lOh.  39m. ;  south  declination  58°  54'. 
In  Halley's  catalogue,  constructed  in  1677,  it  is  marked 


NEW  AND  VARIABLE  STARS.  171 

as  of  the  fourth  magnitude ;  yet  in  Lacaille's  in  1751,  and 
in  subsequent  catalogues,  it  is  recorded  as  of  the  second 
magnitude.  In  the  interval  from  1811  to  1815,  it  was 
again  of  the  fourth ;  and  again  from  1822  to  1826  of  the 
second  magnitude.  In  1827,  it  increased  to  the  first 
magnitude ;  it  thence  receded  to  the  second,  and  so  con- 
tinued until  the  end  of  1837.  In  the  beginning  of  1838, 
it  suddenly  increased  in  luster  so  as  to  surpass  all  the 
stars  of  the  first  magnitude  except  Sirius,  Canopus,  and 
Alpha  Centauri,  which  last  star  it  nearly  equaled. 
Thence  it  again  diminished,  and  in  1842,  it  was  pro- 
nounced by  Maclear  as  inferior  to  Alpha  Crucis,  but  the 
next  year  it  again  revived,  and  became  nearly  equal  to 
Sirius. 

These  facts  afford  abundant  materials  for  speculation. 
The  changes  of  brightness  of  TJ  Argus  are  spread  over 
centuries,  and  apparently  without  any  regular  period. 
What  can  be  the  cause  of  these  changes  ?  To  this  ques- 
tion we  are  unable  to  assign  any  satisfactory  answer, 
and  must  wait  patiently  until  a  greater  accumula- 
tion of  facts  shall  afford  us  a  more  certain  basis  for  a 
theory. 

Several  instances  are  on  record  of  temporary  stars, 
which  have  suddenly  become  visible,  and  after  remaining 
a  while,  apparently  immovable,  have  died  away  and  left 
no  trace  behind.  Such  a  star  is  said  to  have  appeared 
about  the  year  125  B.  C.  Such  stars  are  also  recorded 
in  the  years  A.  D.  389,  945,  1264,  1572,  1604,  and  1670. 
A  similar -phenomenon  has  recently  taken  place.  On  the 


172  HISTORY  OF  ASTRONOMY. 

27th  of  April,  1848,  Mr.  Hind,  of  London,  observed  a 
star  of  the  sixth  magnitude  in  the  constellation  Ophiu- 
chus,  where  he  was  certain  that,  up  to  the  5th  of  that 
month,  no  star  as  bright  as  the  ninth  magnitude  pre- 
viously existed.  Neither  has  any  record  been  discovered 
of  a  star  being  there  observed  at  any  previous  time.  Its 
place  was  in  right  ascension,  16h.  51m.  Is.,  south  declina- 
tion, 12°  39'  14".  On  the  2d  of  May  he  estimated  it  to 
be  of  the  fifth  magnitude,  or  a  little  brighter,  and  there- 
fore distinctly  visible  to  the  naked  eye.  Its  light  was 
reddish  in  the  telescope  ;  and  Dr.  Petersen  observed  that 
the  reddish  color  at  times  increased  suddenly  in  intensity, 
and  again  as  suddenly  disappeared.  Other  observers  no- 
ticed these  peculiar  red  flashes.  On  the  19th  of  May,  Mr. 
Hind  pronounced  it  fainter  than'when  he  first  noticed  it ; 
and  on  the  24th,  it  was  ranked  as  a  star  of  the  sixth  mag- 
nitude. The  Messrs.  Bond,  at  Cambridge,  made  a  series 
of  comparisons  between  this  star  and  one  of  the  fifteenth 
magnitude  in  its  vicinity,  and  found  that  during  three 
months  of  observation  its  position  remained  unchanged. 
They  remarked,  "This  star  resembles  An  tares,  but  its 
red  is  deeper.  It  is  one  of  the  most  strikingly  colored 
stars  we  remember  to  have  seen.  "With  a  power  of  1500 
it  showed  no  sign  of  a  planetary  disc."  On  the  15th  of 
August  they  state,  "  This  star  appears  to  have  decreased 
in  brilliancy,  and  is  now  of  the  seventh  magnitude ;  its 
ruby  red  color  still  remains.  It  is  at  once  recognized 
from  its  neighbors  by  its  color  alone."  On  the  23d  of 
March,  1849,  Professor  Kendall,  of  Philadelphia,  pro- 


NEW  AND  VARIABLE  STARS.  173 

notmced  this  star  to  be  of  the  eightfi  magnitude.  On  the 
evening  of  June  4th,  1850,  the  writer  made  a  careful  sur- 
vey of  all  the  stars  in  this  vicinity,  and  found  only  one 
which  could  be  estimated  as  high  as  the  tenth  magnitude, 
and  this  had  no  very  decided  red  color.  Hind's  star  may 
therefore  now  be  pronounced  extinct. 

Hind's  star  was  not  many  degrees  distant  from  the 
place  where  a  new  star  was  seen  in  1604.  This  star  was 
first  announced  on  the  10th  of  October,  and  it  was  seen  by 
Kepler  on  the  17th.  The  star  was  perfectly  round,  with- 
out nebulosity  or  tail ;  its  light  was  brighter  and  more  un- 
steady than  that  of  the  other  stars.  After  it  had  risen  above 
the  vapors  of  the  horizon,  its  light  was  white.  It  not  only 
surpassed  stars  of  the  first  magnitude,  but  also  Mars  and 
Jupiter.  Some  even  compared  it  to  Yenus,  but  Kepler 
was  not  of  this  opinion.  Observations  proved  that  it  had 
no  motion  or  sensible  parallax.  On  the  9th  of  November 
it  was  seen  in  a  twilight  which  rendered  Jupiter  invisible. 
On  the  Itfth,  Kepler  saw  it  for  the  last  time,  before  its 
conjunction  with  the  sun.  On  the  24th  of  December,  it 
reappeared  in  the  east  with  diminished  brightness.  It 
was  still  brighter  than  Antares,  but  inferior  to  Arcturus. 
On  the  20th  of  March  it  appeared  smaller  than  Saturn ;  but 
it  was  much  larger  than  the 'stars  of  the  third  magnitude 
in  Ophiuchus.  On  the  13th  of  September  it  was  smaller 
than  the  third  magnitude,  and  on  the  8th  of  October  it 
could  be  seen  with  difficulty.  A  few  days  later  it  disap- 
peared in  the  sun's  rays.  In  January  and  February  some 
observers  thought  they  saw  this  star  again,  but  without 


174  HISTORY  OF  ASTRONOMY. 

being  confident  of  it.  In  the  month  of  March  it  could 
not  possibly  be  seen,  so  that  it  must  have  disappeared  be- 
tween October,  1605,  and  February,  1606.  Mr.  Hind's 
star  is  about  12°  north  of  the  place  of  that  discovered 
in  1604,  and  about  17  minutes  of  time  less  in  right  ascen- 
sion. 

Mr.  Hind  has  recently  announced  another  scarlet  star, 
between  Orion  and  Eridanus.  Its  place  is  in  right  as- 
cension 4h.  52m.  45s.,  declination  12°  2'  south.  He  says, 
"I  found  this  star  in  October,  1845,  and  have  kept  a  close 
watch  upon  it  since.  It  is  of  about  the  seventh  magni- 
tude, and  the  most  curious  colored  object  I  have  seen." 

In  November,  1850,  Mr.  Hind  discovered  a  new  star  of 
the  seventh  magnitude,  of  a  fiery  color,  with  a  dull  plan- 
etary aspect.  Its  place  was  in  right  ascension  Ih.  22m. 
54s.,  declination  2°  6'  north.  This  star  is  not  in  the 
Histoire  Celeste,  or  Bessel's  Zones;  nor  does  it  occur  on 
the  star  maps  of  the  Berlin  Academy. 

Mr.  Hind,  in  the  course  of  his  observations  in  search 
of  planets,  has  discovered  fifteen  new  variable  stars.  Prob- 
ably most  of  these  will  be  found  to  belong  to  the  class 
of  periodical  stars. 


SECTION  III. 

DISTRIBUTION  OP  THE  STARS  IN  SPACE. 

BEFORE  the  invention  of  the  telescope,  it  was  impossible 
to  acquire  a  very  precise  knowledge  of  the  distance  of 
the  stars  and  their  distribution  in  space ;  and  even  after 
the  invention  of  the  telescope,  no  one  attempted  to  use  it 
in  any  adequate  manner  to  determine  the  constitution  of 
the  heavens,  until  the  time  of  Sir  William  Herschel.  This 
astronomer,  having  the  command  of  instruments  far  supe- 
rior to  any  who  had  preceded  him,  undertook  a  series  of 
exact  observation,  upon  which  to  found  a  knowledge  of 
the  starry  heavens.  In  1784  he  first  advanced  an  hypo- 
thesis respecting  the  Milky  Way,  which  was  substantially 
as  follows :  The  stars  of  our  firmament,  instead  of  being 
scattered  in  all  directions  indifferently  through  space,  con- 
stitute a  cluster  with  definite  limits,  in  the  form  of  a 
stratum,  of  which  the  thickness  is  small  in  comparison 
with  its  length  and  breadth;  and  in  which  the  earth 
occupies  a  space  somewhere  about  the  middle  of  its  thick- 
ness, and .  near  the  point  where  it  subdivides  into  two 
principal  laminae,  inclined  at  a  small  angle  to  each  other. 
For,  to  an  eye  so  situated,  the  apparent  density  of  the 
stars,  supposing  them  pretty  equally  scattered  through  the 


176  HISTOKY  OF  ASTKONOMY. 

space  they  occupy,  would  be  least  in  the  direction  of  a 
visual  ray  perpendicular  to  the  lamina,  and  greatest  in 
that  of  its  breadth ;  increasing  rapidly  in  passing  from 
one  to  the  other  direction,  just  as  we  see  a  slight  haze  in 
the  atmosphere  thickening  into  a  decided  fog-bank  near 
the  horizon,  by  the  rapid  increase  of  the  mere  length  of 
the  visual  ray. 


Herschel  was  conducted  to  this  view  of  the  Milky  Way 
by  the  following  considerations.  Supposing  the  stars  to 
be  situated,  in  general,  at  equal  distances  from  each  other, 
the  number  of  stars  observed  in  the  field  of  a  telescope 
ought  to  be  about  the  same  in  all  possible  directions,  pro- 
vided the  stars  extend  in  all  directions^  to  the  same  dis- 
tance. But  if  we  have  a  stratum  of  stars  at  equal  dis- 
tances from  each  other,  of  a  form  whose  thickness  is  small 
in  comparison  with  its  diameter,  then  the  number  of  stars 
visible  in  the  different  directions,  will  lead  us  to  a  knowl- 
edge both  of  the  exterior  form  of  the  starry  stratum,  and 
of  the  place  occupied  by  the  observer.  For  example,  if 
within  a  certain  circle  of  the  heavens  we  count  ten  stars, 
and  in  a  circle  of  the  same  diameter,  taken  in  a  different 
direction,  we  count  eighty  stars  with  the  same  telescope, 
the  lengths  of  the  two  visual  rays  will  be  in  the  ratio  of 
1  to  2,  or  the  cube  roots  of  1  and  8.  This  is  substantially 
Herschel's  method  of  star-gages,  in  which  he  employed  a 


DISTBIBUTION  OF  THE  STAHS.  177 

telescope  of  18  inches  aperture,  with  a  field  of  view  of 
about  a  quarter  of  a  degree.  Herschel  made  3400  gages 
of  this  kind.  These  gages  indicate  the  number  of  stars 
visible  in  the  field  of  his  telescope,  and  from  this  number 
he  deduced  the  corresponding  lengths  of  the  visual  rays. 
Assuming  the  distance  of  the  nearest  of  the  fixed  stars  in 
accordance  with  the  estimate  of  Struve,  we  find  that, 
according  to  Herschel,  the  stars  upon  the  borders  of  our 
stratum,  in  the  constellation  of  the  Eagle,  are  at  such  a 
distance  as  light  requires  7000  years  to  traverse — and 
from  the  remoter  stars,  light  would  require  13,000  years 
to  come  to  us. 

The  figure  on  the  next  page  is  designed  to  represent 
the  form  of  the  nebula  in  which  our  own  solar  system  is 
placed,  according  to  the  views  advanced  by  Sir  "William 
Herschel. 

The  great  nebulae  of  the  heavens,  such  as  those  of  Orion 
and  Andromeda,  Herschel  conjectured  to  be  Milky  Ways 
like  our  own,  only  of  much  superior  dimensions.  The 
nebula  of  Andromeda,  which  he  concluded  to  be  the  near- 
est, he  placed  at  a  distance  2000  times  greater  than  that 
of  stars  of  the  first  magnitude. 

This  hypothesis  respecting  the  phenomena  of  the  Milky 
Way,  would  be  tenable,  provided  it  were  true,  1st,  that 
the  stars  are  uniformly  distributed  through  space ;  and  2d, 
that  Herschel  was  able,  with  his  telescope  of  20  feet,  to 
penetrate  to  the  limits  of  our  stratum. 

With  regard  to  the  first  of  these  hypotheses,  we  find 
that  Herschel  himself  subsequently  abandoned  it  as  unten- 

•  8* 


DISTRIBUTION  OF  THE  STARS.  179 

able.  In  1796,  he  says,  "  The  hypothesis  of  a  uniform 
distribution  of  the  stars  is  too  far  from  the  exact  truth,  to 
serve  as  a  basis  in  this  research."  Again,  in  1811,  he 
adds,  "The  uniform  distribution  of  the  stars  may  be  ad- 
mitted in  certain  calculations ;  but  when  we  examine  the 
Milky  "Way,  this  equal  distribution  must  be  abandoned.'11 
And  in  1817  he  says,  "  Although  an  increased  number 
of  stars  in  the  field  of  the  telescope  is  generally  an  indi- 
cation of  their  greater  distance,  my  gages  refer  more  directly 
to  the  degree  of  condensation  of  the  stars" 

As  to  the  second  of  the  above  conditions,  viz.,  that  in 
his  gages  he  was  able  to  penetrate  to  the  extreme  limits 
of  the  Milky  Way,  Herschel's  views  underwent  an  entire 
change  in  the  progress  of  his  researches.     In  1817,  speak- 
ing of  some  of  his  gages,  he  says,  "It  is  plain  that  the 
extreme  penetrating  power  of  the  20  feet  telescope  was 
insufficient   to  sound  the   depth  of   the  Milky  "Way." 
Again,  in  1818,  he  says,  "  In  these  ten  observations  the 
gages  were  arrested  in  their  progress  by  the  extreme  faint- 
ness  of  the  stars.     There  is,  however,  no  doubt  respecting 
the  further  extent  of  the  starry  region.     For  if  in  one  of 
the  observations,  a  feeble  nebulosity  had  been  suspected, 
the  application  of  a  higher  magnifying  power  showed  that 
the  doubtful  appearance  was  caused  by  the  blending  of 
numerous  stars,  too  small  to  be  seen  by  the  aid  of  a  lower 
magnifying  power.     "We  hence  infer  that  if  our  gages 
cease  to  resolve  the  Milky  "Way  into  stars,  it  is  not  be- 
cause its  nature  is  doubtful,  but  because  it  is  fathomless." 
Thus  we  see  that  the  hypothesis  which  Herschel  an- 


180  HISTORY  OF  ASTRONOMY. 

nounced  in  1785,  with,  regard  to  the  constitution  of  the 
Milky  Way,  and  which  .is  still  connected  with  Her- 
schel's  name  in  almost  all  the  popular  treatises  on  as- 
tronomy, was  afterward  substantially  abandoned  by  its 
author. 

Quite  recently,  M.  Struve,  of  Pulkova,  has  undertaken 
a  discussion  of  the  same  subject,  employing,  as  the  basis 
of  his  researches,  the  most  extensive  catalogues  of  stars. 
He  has  determined,  partly  by  enumeration,  and  partly  by 
estimation,  the  number  of  stars  of  each  class,  as  far  as  the 
ninth  magnitude,  and  their  distribution  throughout  the 
heavens.  He  finds  that  these  stars  are  not  uniformity 
distributed ;  but  that  near  the  equator  they  are  most 
abundant,  in  the  neighborhood  of  two  points  almost 
diametrically  opposed,  viz.,  in  right  ascension  6h.  40m., 
and  18h.  40m.  The  stars  are  least  abundant  near  the 
diameter  passing  through  Ih.  30m.,  and  13h.  30m.  This 
diameter  makes  an  angle  of  78°  with  the  preceding.  The 
diameter  of  greatest  condensation  coincides  almost  exactly 
with  the  position  of  the  Milky  "Way ;  thus  proving  that 
the  phenomena  of  the  Milky  "Way  are  intimately  con- 
nected with  the  distribution  of  the  stars  from  the  first  to 
the  ninth  magnitudes,  or  rather  that  the  two  phenomena 
are  identical.  Herschel  proved,  in  1817,  that  the  Milky 
Way  was  fathomless,  even  with  his  telescope  of  40  feet. 
The  same  uncertainty  respecting  the  limits  of  the  visible 
stars  exists  in  every  part  of  the  heavens,  even  toward  the 
poles  of  the  Milky  Way.  Hence,  if  we  regard  all  the  fixed 
stars  which  surround  the  sun  as  forming  one  grand  system. 


DISTRIBUTION   OF  THE  STAES.  181 

that  of  the  Milky  Way,  we  are  entirely  ignorant  of  its  extent, 
and  have  not  the  least  idea  of  the  external  form  of  this  im- 
mense .system. 

The  two  opposite  points  of  the  celestial  sphere  around 
which  the  stars  are  observed  to  be  most  sparse,  have  been 
called  the  Galactic  Poles;  and  the  great  circle  at  right 
angles  to  the  diameter  joining  these  points,  has  been  de- 
•nominated  the  Galactic  Circle.  For  convenience,  we  will 
express  the  distance  of  different  points  of  the  firmament 
from  the  galactic  circle,  in  either  hemisphere,  by  the  terms 
north  or  south  Galactic  Latitude. 

The  observations  made  in  the  northern  hemisphere  by 
Sir  W.  Herschel,  and  subsequently  continued  in  the 
southern  hemisphere  by  Sir  J.  Herschel,  have  supplied 
data  for  determining  the  law  of  the  distribution  of  the 
stars  according  to  their  galactic  latitude.  The  telescope 
used  in  these  observations  had  18  inches  aperture,  20 
feet  focal  length,  and  a  magnifying  power  of  180.  It  was 
directed  indiscriminately  to  every  part  of  the  celestial 
sphere,  visible  in  the  latitude  of  the  places  of  observa- 
tion. The  observations  of  Sir  J.  Herschel  were  made 
during  his  residence  at  the  Cape  of  Good  Hope,  in  the 
years  1834-8.  About  2300  gages  were  obtained,  dis- 
tributed with  tolerable  impartiality  over  the  southern 
heavens. 

An  analysis  of  the  observations  of  Sir  W.  Herschel  was 
made  by  Professor  Struve,  with  a  view  of  determining 
the  mean,  density  of  the  stars  in  successive  zones  of  galac- 
tic latitude ;  and  a  similar  analysis  has  been  made  of  the 


182  HISTORY  OF  ASTRONOMY. 

observations  of  Sir  J.  Herschel.  If  we  imagine  the  celes- 
tial sphere  to  be  divided  into  a  series  of  zones,  each  meas- 
uring 15°  in  breadth,  and  bounded  by  parallels  to  the 
galactic  circle,  the  average  number  of  stars  included 
within  a  circle  15'  in  diameter  will  be  that  which  is 
given  in  the  second  column  of  the  following  table. 

Galactic  Latitude.  Average  number  of  stars  in  a 

circle  15'  in  diameter. 

90°— 75°  North.        .        .    '    \  li   ^    .      4.32 
75o_60o      tt  ......       5.42 

60° — 45°      "  8.21 

45o_30o      «  .         .         m-       m         f     13  61 

30°— 15°      u  ......     24.09 

15o_  QQ  .  «  53  43 

Galactic  Circle  122.00 

0°— 15°  South 59.06 

150—300      "  .....     26.29 

30°— 450      «  .....     13.49 

450 — 60°      "  .         .         .        '.    .     .  "    9.08 

60°—75°      «  .....       6.62 

750—90°      ««  6i05 

It  appears,  therefore,  that  the  variation  of  density  of 
the  visible  stars,  in  proceeding  from  the  galactic  poles,  is 
subject  to  almost  exactly  the  same  law  of  decrease  in 
either  hemisphere;  the  density  being,  however,  some- 
what greater  in  the  southern  than  in  the  northern  hemi- 
sphere. 

M.  Struve  has  attempted  to  form  an  estimate  of  the  rel- 
ative distances  of  stars  of  the  different  magnitudes  as  de- 
duced from  their  number,  supposing  the  stars  to  be  dis- 


DISTRIBUTION   OF  THE  STARS. 


183 


tributed  at  uniform  distances  from  each  other  along  the 
middle  of  the  Milky  Way,  and  obtained  the  following  re- 
sults: 


Magnitude  of  stars. 

Mean  distance. 

Magnitude  of  stars. 

Mean  distance. 

1 

.    .  i-oooo 

6     ... 

.       7-7258 

2 

1-8031 

7    ... 

.     11-3262 

3 

2-7639 

8     ... 

,     19-6405 

4 

3-9057 

9    . 

.     31-2904 

5       ;  *: 

5-4545 

12     . 

.  227-7820 

According  to  this  table,  the  distance  of  stars  of  the  sixth 
magnitude,  which  are  just  visible  to  the  naked  eye,  is 
about  eight  times  as  great  as  that  of  stars  of  the  first  mag- 
nitude. The  distance  of  stars  of  the  twelfth  magnitude, 
by  which  is  meant  those  stars  which  were  barely  visible 
in  Herschel's  twenty  feet  telescope,  is  228  times  as  great 
as  that  of  stars  of  the  first  magnitude. 

Assuming  the  preceding  relative  distances,  and  also 
that  the  average  parallax  of  a  star  of  the  second  magni- 
tude is  0".116,  we  obtain  the  absolute  distance  of  stars  of 
each  magnitude  as  given  on  page  168. 

Professor  Encke,  of  Berlin,  has  criticized  these  specula- 
tions of  Sfruve  with  some  severity.  He  thinks  that 
they  involve  several  hypotheses  which  are  altogether 
unwarrantable.  They  assume, 

I.  That  the  apparent  brightness  of  the  stars  is  the 
simple  effect  of  distance,  so  that  we  can  assign  the 
radius  of  the  sphere  within  which  the  stars  of  each  class 
are  comprised.  Encke  objects  to  this  assumption,  1.  That 
it  is  contrary  to  the  analogy  of  our  solar  system,  in 
which  the  magnitudes  of  the  planets  are  very  unequal. 


184  HISTOEY  OF  ASTRONOMY. 

2.  It  is  contradicted  by  the  parallax  of  the  stars  so  far  as 
the  same  has  been  determined.  The  parallax  of  several 
stars  of  the  fifth  and  sixth  .magnitudes  is  greater  than 
that  of  most  stars  of  the  first  magnitude.'  The  star  61 
Cygni,  of  the  fifth  magnitude,  has  a  parallax  certainly 
greater  than  what  Struve  has  given  for  the  average 
parallax  of  stars  of  the  first  magnitude.  3.  It  is  contra- 
dicted by  the  phenomena  of  the  binary  stars.  There  is 
a  large  number  of  double  stars,  which  are  proved  to  be 
physically  connected,  and  therefore  both  are  situated  at 
nearly  the  same  distance  from  the  earth,  while  in  most 
of  them  there  is  a  perceptible  disparity  of  brightness, 
and  in  some  cases  this  disparity  amounts  to  four  mag- 
nitudes. 

II.  The  distribution  of  the  stars  over  the  entire  heavens 
is  admitted  not  to  be  uniform,  nevertheless  such  a 
uniform  distribution  is  assumed  for  the  plane  of  the 
Milky  Way,  and  the  irregularities  which  we  observe  in 
it  are  regarded  as  in  part  unimportant,  and  in  part 
ascribed  to  the  eccentric  position  of  the  sun,  and  its.  dis- 
tance from  the  plane  of  the  Milky  Way.  Hence  it  is  in- 
ferred that  from  the  number  of  the  stars  of  a  given  bright- 
ness, we  may  determine  the  ratio  of  the  radius  of  their 
sphere  to  that  of  stars  of  any  other  brightness. 

These  and  several  other  hypotheses  which  are  involved 
in  Struve's  reasoning,  Professor  Encke  regards  as  alto- 
gether inadmissible,   and  he  concludes  that   the   mean 
parallax  which  Struve  ascribes  to  stars  of  the  first  mag 
nitude  (viz.  0".209)  is  entirely  unworthy  of  confidence. 


DISTRIBUTION  OF  THE  STABS.  185 

Sir  J.  Herschel  has  computed  from  his  gages,  that  the 
number  of  stars  visible  enough  to  be  distinctly  counted 
in  the  twenty  feet  reflector,  in  both  hemispheres,  is  about 
Jive  and  a  half  millions.  That  the  actual  number  is  much 
greater  than  this,  he  infers  from  the  fact  that  there  are 
large  tracts  of  the  Milky  "Way  so  crowded  as  to  defy 
counting  the  gages,  not  by  reason  of  the  smallness  of  the 
stars,  but  on  account  of  their  number. 

Sir  J.  Herschel,  in  counting  the  gages,  not  only  set 
down  the  total  number  of  stars,  but  the  number  for  each 
magnitude  down  to  the  eleventh,  and  even  for  the  es- 
timated half-magnitudes.  Upon  classifying  the  stars 
according  to  their  magnitudes,  it  appears  that  the  increase 
of  density  in  approaching  the  Milky  "Way  is  quite  im- 
perceptible among  stars  of  a  higher  magnitude  than  the 
eighth,  and  except  on  the  very  verge  of  the  Milky  Way 
itself,  stars  of  the  eighth  magnitude  can  hardly  be  said  to 
participate  in  the  general  law  of  increase.  For  the  ninth 
and  tenth  magnitudes  the  increase,  though  unequivocally 
indicated  over  a  zone  extending  at  least  30°  on  either  side 
of  the  Milky  "Way,  is  by  no  means  striking.  It  is  with 
the  eleventh  magnitude  that  it  first  becomes  conspicuous, 
though  still  of  small  amount  when  compared  with  that 
which  prevails  among  the  mass  of  stars  inferior  to  the 
eleventh,  which  constitute  sixteen  seventeenths  of  the  totality 
of  stars  within  thirty  degrees  on  either  side  of  the  Milky 
Way. 

From  these  observations  Sir  J.  Herschel  draws  the  two 
following  conclusions;  viz. — "1st.  That  the  larger  stars 


186  HISTORY  OF  ASTRONOMY. 

are  really  nearer  to  us  (taken  en  masse,  and  without  deny- 
ing individual  exceptions)  than  the  smaller  ones.  "Were 
this  not  the  case,  were  there  really  among  the  infinite 
multitude  of  stars  constituting  the  remoter  portion  of  the 
galaxy,  numerous  individuals  of  extravagant  size  and 
brightness,  as  compared  with  the  generality  of  those 
around  them,  so  as  to  overcome  the  effect  of  distance,  and 
appear  to  us  as  larger  stars,  the  probability  of  their  oc- 
currence in  any  given  region  would  increase  with  the 
total  apparent  density  of  stars  in  that  region,  and  would 
result  in  a  preponderance  of  considerable  stars  in  the 
Milky  "Way,  beyond  what  the  -heavens  really  present  over 
its  whole  circumference.  2d.  That  the  depth  at  which 
our  system  is  plunged  in  the  sidereal  stratum  constituting 
the  galaxy,  reckoning  from  the  southern  surface  or  limit 
of  that  stratum,  is  about  equal  to  that  distance  which,  on 
a  general  average,  corresponds  to  the  light  of  a  star  of 
the  ninth  or  tenth  magnitude,  and  certainly  does  not 
exceed  that  corresponding  to  the  eleventh." 

This  last  conclusion  seems  clearly  to  assume,  not  only 
that  our  Milky  "Way  consists  of  a  stratum  of  stars  which  has 
determinate  limits,  but  that  these  limits  (at  least  in  certain 
directions)  have  been  indicated  by  observation.  It  does 
not,  however,  appear  that  such  a  conclusion  is  authorized 
by  the  gages.  The  number  of  stars  of  the  smallest  mag- 
nitude visible,  increases  rapidly  even  up  to  the  poles  of 
the  Milky  "Way,  although  this  increase  is  most  rapid  in 
the  middle  zone  of  the  galaxy.  The  gages  therefore  in- 
dicate a  condensation  of  stars  in  the  neighborhood  of  the 


DISTRIBUTION  OF  THE  STABS.  187 

Milky  "Way,  but  not  that  our  telescopes  have  penetrated 
to  the  boundaries  of  our  stratum.  "  Every  increase  in  the 
power  of  our  telescopes  has  hitherto  disclosed  new  stars 
in  every  part  of  the  heavens ;  it  is  therefore  unphiloso- 
phical  to  infer  that  such  would  not  continue  to  be  the 
case  if  we  could  command  a  further  increase  of  telescopic 
power.  It  is,  however,  remarkable  that  those  portions 
of  the  heavens  which  are  most  remote  from  the  Milky 
Way  are  richest  in  nebulae  and  clusters  of  stars.  In  the 
neighborhood  of  the  north  pole  of  the  Milky  Way,  within 
a  region  occupying  about  one  eighth  of  the  whole  surface 
of  the  sphere,  one  third  of  the  entire  nebulous  contents  of 
the  heavens  are  congregated.  A  large  portion  of  these 
nebulas  have  been  resolved  into  clusters  of  stars,  and 
these  stars,  upon  the  principle  that  faintness  is  merely  the 
effect  of  distance,  must  be  inferred  to  be  as  near  to  us  as 
the  faintest  stars  of  the  Milky  Way. 

On  the  whole,  we  must  conclude  that  the  stars,  in  every 
part  of  the  heavens,  extend  to  a  distance  beyond  the  reach 
of  the  most  powerful  telescope  hitherto  constructed ;  that 
therefore  the  shape  of  that  portion  of  space  which  the  stars 
occupy  is  entirely  unknown  to  us ;  that  within  this  space 
the  stars  are  not  uniformily  distributed,  and  are  most 
crowded  in  the  neighborhood  of  a  plane  which  we  call 
the  Milky  Way ;  that  out  of  this  plane  the  stars  exhibit  a 
great  many  centers  of  attraction,  about  which  an  immense 
number  of  them  are  clustered ;  but  that  the  entire  space, 
so  far  as  we  can  perceive,  is  studded,  though  more 
sparsely,  with  stars.  The  material  universe  therefore  ap- 


188  HISTORY    OF  ASTKONOMY. 

pears  to  us  boundless ;  and  astronomers,  certainly  of  the 
present  age,  need  not  be  apprehensive  that  they  will  ever 
witness  the  time  when  there  will  be  no  more  worlds  to 
conquer. 


SECTION  IV. 

MOTION  OF  THE  SUN  AND  FIXED  STARS. 

To  common  observation,  the  fixed  stars  retain  sensibly 
the  same  relative  position  from  age  to  age ;  but  the  ex- 
act observations  of  modern  astronomy  have  detected  a 
relative  motion  in  a  large  number  of  them.  A  small  star 
in  the  leg  of  the  Great  Bear  (called  1830  Groombridge) 
has  an  annual  motion  of  seven  seconds  of  arc  as  compared 
with  neighboring  stars ;  and,  there  are  more  than  thirty 
stars  known,  whose  annual  proper  motion  exceeds  one 
second.  It  might  have  been  expected,  a  priori,  that  mo- 
tion of  some  kind  must  exist  among  such  a  multitude  of 
objects  all  subject  to  mutual  attraction;  and  it  appears 
highly  probable,  not  to  say  certain,  that  the  sun  must 
participate  in  this  movement.  The  effect  of  a  motion 
of  the  sun,  with  reference  to  the  stars,  would  be  an  ap- 
parent divergence  or  separation  of  those  stars  toward 
which  we  were  moving,  and  an  apparent  convergence  or 
closing  up  of  the  stars  in  the  region  which  we  were  leav- 
ing. We  might  therefore  expect  to  detect  such  a  motion, 
if  it  really  exists,  by  comparing  the  proper  motions  of  all 
the  stars  in  the  firmament.  In  accordance  with  this  idea, 
Sir  William  Herschel,  in  1783,  by  a  comparison  of  the 


190  HISTOKY  OF  ASTRONOMY. 

proper  motions  of  such  stars  as  were  then  best  ascertain- 
ed, arrived  at  the  conclusion  that  the  sun  had  a  relative 
motion  among  the  fixed  stars,  in  the  direction  of  a  point 
in  the  constellation  Hercules,  whose  right  ascension  is 
260°  34',  and  declination  26°  17'  north. 

More  recently,  M.  Argelander,  by  comparing  the  proper 
motions  of  390  stars,  has  located  this  point  in  right  as- 
cension 257°  35',  and  declination  36°  3'  north.  M.  Luhn- 
dahl,  by  a  comparison  of  the  proper  motions  of  147 
stars,  has  obtained  for  this  point,  right  ascension,  252° 
53',  declination  14°  26'  north ;  and  M.  Struve,  by  com- 
paring the  proper  motions  of  392  stars,  has  located  this 
point  in  right  ascension  261°  22',  declination  27°  36' 
north.  The  most  probable  mean  of  the  results  of  these 
three  astronomers  is  right  ascension  259°  9',  declination 
34°  37'  north,  which  it  will  be  seen  does  not  differ  greatly 
from  the  point  originally  assigned  by  Sir  ~W.  Herschel. 

Quite  recently  Mr.  Galloway  has  made  a  similar  com- 
parison of  stars  visible  in  the  southern  hemisphere ;  and 
from  the  proper  motion  of  81  southern  stars  not  em- 
ployed in  the  preceding  investigations,  he  has  located 
the  point  toward  which  the  sun  is  moving,  in  right  as- 
cension 260°  1',  declination  34°  23'  north,  a  result  almost 
identical  with  that  obtained  in  the  northern  hemisphere. 

It  seems  then  nearly  certain  that  the  apparent  motion 
of  these  stars  is  due,  at  least  in  part,  to  a  relative  motion 
of  our  sun,  and  the  same  observations  afford  us  the  means 
of  estimating  its  velocity.  According  to  Struve's  calcu- 
lations, this  velocity  is  such  as  would  carry  it  annually 


THE  SUN  AND  FIXED  STARS.  191 

over  an  angle  of  one  third  of  a  second,  if  seen  at  right 
angles  from  the  average  distance  of  a  star  of  the  first 
magnitude.  If  we  assume  the  parallax  of  such  a  star  as 
equal  to  one  fifth  of  a  second,  we  shall  find  that  the  sun 
advances  through  space,  carrying  with  it  the  whole 
system  of  planets  and  comets,  with  a  velocity  about  one 
fourth  of  the  earth's  annual  motion  in  its  orbit. 

A  great  many  questions  here  naturally  suggest  them- 
selves. Is  the  sun's  motion  uniform  and  rectilinear,  or 
is  it  moving  slowly  in  an  orbit  about  some  center  ?  Are 
the  stars  moving  in  straight  lines,  or  in  grand  orbits? 
Have  all  the  stars,  including  our  sun,  a  common  move- 
ment of  rotation  about  some  general  center?  This  ques- 
tion has  been  examined  by  Professor  Madler  of  the 
Dorpat  observatory,  and  he  has  attempted  to  assign  the 
center  round  which  the  sun  and  stars  revolve,  which 
center  he  places  in  the  group  of  the  Pleiades. 

If  we  assume  that  the  orbit  described  by  our  sun 
about  the  central  point  is  a  circle,  this  central  point  must 
be  found  on  the  circumference  of  a  great  circle,  whose 
pole  is  that  point  toward  which  the  sun  is  moving,  in 
right  ascension  259^°,  declination  34£°  north.  This  circle 
cuts  the  Milky  Way  in  the  constellation  Perseus,  and 
Argelander  conjectured  the  central  point  to  be  here  in 
Perseus.  The  most  remarkable  cluster  of  stars  in  this 
neighborhood  is  the  Pleiades,  and  Madler  conjectured 
that  here  might  be  the  central  point.  Accordingly  he 
determined  the  proper  motion  of  the  eleven  principal 
stars  in  this  cluster  by  comparing  the  observations  of 


192  HISTORY  OF  ASTRONOMY. 

Bessel  with  those  of  Bradley  and  other  astronomers. 
These  motions  exhibit  considerable  uniformity,  and  their 
direction  is  invariably  toward  the  south. 

Madler  next  examined  the  12  principal  stars  within 
five  degrees  of  this  group,  and  finds  that  8  exhibit  a 
decided  southern  motion,  while  in  the  other  4  the  motion 
is  too  small  to  be  decisive,  but  in  no  case  is  the  motion 
toward  the  north.  Among  thirty  stars,  between  5  and 
10  degrees  distant  from  the  Pleiades,  Madler  finds  that 
20  are  moving  toward  the  south ;  while  the  motion  of 
the  remaining  10  is  scarcely  perceptible.  Among  57 
stars,  between  10  and  15  degrees  from  the  Pleiades,  16 
are  moving  toward  the  south,  while  the  motion  of  the 
remaining  41  is  scarcely  perceptible.  Not  one  moves 
toward  the  north.  Out  of  66  stars,  between  15  and  20 
degrees  from  the  Pleiades,  30  have  a  decided  southern 
motion,  and  36  are  undecided.  Thus,  out  of  176  stars, 
within  20  degrees  of  the  Pleiades,  we  find  85  moving 
toward  the  south,  and  91  whose  motion  is  scarcely  per- 
ceptible, but  not  a  single  case  in  which  there  is  a  con- 
siderable motion  toward  the  north. 

Madler  next  examined  all  of  Bradley's  stars  between 
20  and  30  degrees  from  the  Pleiades,  of  which  the  number 
is  175  ;  of  these,  78  exhibit  a  motion  toward  the  south, 
92  are  uncertain,  and  5  have  a  slow  motion  toward  the 
north,  amounting  in  the  most  rapid  case  to  only  seven 
seconds  in  a  century.  Such  a  result  Professor  Madler 
considers  a  necessary  consequence  of  his  hypothesis. 
Since  only  small  real  motions  are  to  be  expected  in  the 


THE  SUN  AND  FIXED  STABS.  193 

neighborhood  of  the  central  point,  the  motions,  which 
are  only  apparent,  and  therefore  contrary  to  the  solar 
motion,  must  preponderate  for  all  stars  between  the  sun 
and  the  Pleiades. 

The  most  rapid  proper  motions,  according  to  this 
hypothesis,  must  be  sought  for  near  the  great  circle 
described  about  the  Pleiades  as  a  pole ;  and  accordingly 
we  find  near  this  circle  two  of  the  most  decided  of  all 
the  proper  motions  hitherto  discovered. 

Professor  Madler  accordingly  infers  that  the  central 
point  of  the  starry  heavens  must  be  placed  in  the  neigh- 
l»orhood  of  the  Pleiades.  This  group  is  the  nearest,  the 
brightest,  and  the  richest  cluster  in  the  whole  heavens. 
Moreover,  Alcyone  is  the  optical  center  of  this  group, 
:ind  he  infers  that  this  is  the  star  which  combines  the 
strongest  probability  of  being  the  true  central  sun. 

Alcyone,  known  also  as  TJ  Tauri,  or  25  Tauri,  is  a 
double  star  of  the  third  or  fourth  magnitude,  in  right 
ascension  3h.  38m.,  declination  23°  39'  north. 

Assuming  the  parallax  of  61  Cygni,  as  determined  by 
Bessel,  and  that  the  sun  and  this  star  are  moving  with 
the  same  velocity  about  Alcyone,  Madler  has  computed 
that  the  distance  of  Alcyone  is  34  millions  of  times  that 
of  the  sun,  requiring  537  years  for  its  light  to  come  to 
us,  although  moving  at  the  rate  of  twelve  millions  of 
miles  per  minute.  The  periodic  time  of  the  sun  about 
Alcyone  is  estimated  at  18  millions  of  years ;  and  the 
sum  of  the  masses  of  all  the  stars  within  the  sphere 
described  about  Alcyone  as  a  center,  with  a  radius  equal 


194  HISTOEY  OF  ASTRONOMY. 

to  the  sun's  distance,  is  117  million  times  the  mass  of  the 
sun. 

The  preceding  conclusions  are  certainly  wonderful ; 
but,  unfortunately,  they  rest  upon  a  very  unsatisfactory 
basis.  Professor  Madler  has  subjected  the  stars  in  the 
neighborhood  of  Alcyone  to  a  very  careful  examination, 
and  finds  decisive  indications  of  the  sun's  relative  motion, 
as  it  had  been  previously  established  by  the  labors  of 
Argelander  and  others.  But  beyond  the  neighborhood  of 
the  Pleiades,  the  number  of  stars  examined  is  altogether 
too  small  to  form  the  basis  of  so  important  conclusions. 
Sir  John  Herschel  pronounces  it  almost  inconceivable, 
that  any  general  circulation  of  the  stars  can  take  place 
out  of  the  plane  of  the  Milky  Way,  while  the  Pleiades 
are  situated  20  degrees  out  of  this  plane.  It  is  not,  how- 
ever, presumptuous  to  expect  that  the  problem  which 
Madler  has  propounded  will  one  day  be  resolved.  A 
careful  determination  of  the  proper  motion  of  a  con- 
siderable number  of  stars  suitably  situated  in  different 
parts  of  the  heavens,  could  not  fail  to  settle  the  question. 

M.  Struve  has  made  a  careful  comparison  of  the  places 
of  the  stars  observed  at  Dorpat,  with  their  places  as  de- 
termined by  other  astronomers,  for  the  purpose  of  dis 
covering  their  proper  motion.  The  whole  number  of 
stars  which  formed  the  subject  of  research  amounted  to 
1662,  of  which  there  were  734  single  stars  and  928  double 
stars.  From  these  researches,  M.  Struve  concludes  that 
the  angular  motions  of  the  different  classes  of  stars  are 
inversely  proportional  to  their  distances,  from  which  he 


THE  SUN  AND  FIXED  STABS.  195 

infers  that  their  linear  motions  are  equal.  This  he  found 
to  be  true  for  stars  situated  in  every  direction  of  the 
heavens,  by  a  comparison  of  the  proper  motions  of  the 
stars  in  the  different  hours  of  right  ascension. 

The  following  table  is  founded  on  an  examination  of 
the  proper  motions  of  the  stars  of  different  magnitudes  as 
deduced  by  M.  Struve. 

MEAN  MOTION  IN  ONE  HUNDRED  YEARS. 

Magnitude.  Isolated  Stars.                                   Binary  Stars. 

R.A.  Dec.  R.A.  Dec. 

1  .  .  34".2  29".0  .  .  55".5  47".0 

2  .  .  18".9  16".l  .  .  30".8  26".l 

3  .  .  12'U  10".5  .  .  20".l  17".0 

4  .  .  8".f  V'A  .  .  14".2  12".  0 

5  .  .  6".3  5".3  .  .  10".2  8".6 

6  .  .  3".Y  3".l  .  .          6".0  5".l 

7  .  .  2".2  1".8  .  .          3".5  3".0 

8  .  .  1".4  1".2  .  .          2".3  2  .0 

9  .  .  1".0  0".9                           1'.7  1".5 


SECTION  V. 

RESOLUTION  OF  REMABKABLE  NEBULJB. 

THE  last  few  years  have  been  remarkable  for  the  pro- 
duction of  the  largest  telescope  ever  manufactured.  Sir 
"William  Herschel  constructed,  with  his  own  hands,  tele- 
scopes of  20  and  40  feet  focus,  with  which  he  made  some 
of  the  most  brilliant  discoveries  recorded  in  the  history 
of  astronomy.  But  quite  recently,  the  Earl  of  Kosse  has 
completed  a  telescope  still  more  gigantic  than  the  largest 
of  Sir  William  Herschel.  He  had  previously  constructed 
a  telescope  of  three  feet  aperture,  which,  received  the 
highest  commendation  from  Dr.  Robinson  and  Sir  James 
South.  In  1842,  he  commenced  another  of  far  superior 
dimensions,  whose  speculum  was  six  feet  in  diameter, 
and  weighed  three  tons.  The  materials  of  which  it  is  com- 
posed are  copper  and  tin,  united  in  the  proportion  of  fif- 
teen parts  of  copper  to  seven  of  tin.  The  process  of 
grinding  was  conducted  under  water,  and  the  moving 
power  employed  was  a  steam  engine  of  three  horse  power. 
The  substance  made  use  of  to  wear  down  the  surface  was 
emery  and  water,  and  it  required  six  weeks  to  grind  it  to 
a  fair  surface. 

The  tube  of  the  telescope  is  56  feet  long,  and  is  made 


RESOLUTION  OF  REMARKABLE  NEBULJS.  197 

of  wood  one  inch  thick,  and  hooped  with  iron.  The 
diameter  of  this  tube  is  7  feet.  At  12  feet  distance  on 
each  side  of  the  telescope,  a  wall  is  built,  72  feet  long,  48 
high  on  the  outer  side,  and  56  on  the  inner,  the  walls  be- 
ing 24  feet  distant  from  each  other,  and  lying  exactly  in 
the  meridian.  "When  directed  to  the  south,  the  tube  may 
be  lowered  till  it  becomes  almost  horizontal ;  but  when 
pointed  to  the  north,  it  only  falls  till  it  is  parallel  with 
the  earth's  axis.  Its  lateral  movements  take  place  only 
from  wall  to  wall,  and  this  commands  a  view  for  half  an 
hour  on  each  side  of  the  meridian ;  that  is,  the  whole  of 
its  motion  from  east  to  west  is  limited  to  15  degrees.  The 
expense  of  this  instrument  was  not  less  than  twelve  thou- 
sand pounds.  It  has  a  reflecting  surface  of  4071  square 
inches,  while  that  of  Herschel's  40  feet  telescope  had  only 
1811  square  inches. 

In  March,  1845,  Sir  James  South  made  a  trial  of  this 
telescope,  and  gives  the  following  account  of  his  observa- 
tions :  "  Never  before  in  my  life  did  I  see  such  glorious 
sidereal  pictures  as  this  instrument  afforded  us.  The 
most  popularly  known  nebulse  observed  were  the  ring 
nebula  in  the  Canes  Yenatici,  which  was  resolved  into 
stars  with  a  magnifying  power  of  548,  and  the  94th  of 
Messier,  which  is  in  the  same  constellation,  and  which 
was  resolved  into  a  large  globular  cluster  of  stars,  not 
much  unlike  the  well-known  cluster  in  Hercules.  On 
subsequent  nights,  observations  of  other  nebulae,  amount- 
ing to  some  thirty  or  more,  removed  most  of  these  from 
the  list  of  nebulas,  where  they  had  long  figured,  to  that 


198  HISTORY  OF  ASTEONOMY. 

of  clusters ;  while  some  of  these  latter  exhibited  a  sidereal 
picture  in  the  telescope  such  as  man  before  had  never  seen, 
and  which,  for  its  magnificence,  baffles  all  description." 

In  the  Philosophical  Transactions  for  1844,  Lord  Kosse 
has  given  some  observations  of  nebulae  made  with  his 
three  feet  speculum,  accompanied  with  drawings  of  the 
most  remarkable  objects.  Among  these  is  one  which 
Sir  John  Herschel  had  figured  as  an  oval  resolvable 
nebula.  Lord  Eosse's  telescope  exhibits  it  with  resolvable 
filaments  singularly  disposed,  springing  principally  from 
its  southern  extremity,  and  not,  as  is  usual  in  clusters, 
irregularly  in  all  directions.  It  is  studded  with  stars, 
mixed,  however,  with  a  nebulosity,  probably  consisting 
of  stars  too  minute  to  be  recognized.  This  has  been 
called  the  crab  nebula. 

The  Dumb  Bell  nebula,  known  everywhere  by  the 
drawing  of  Sir  John  Herschel,  is  seen  to  consist  of  in- 
numerable stars  mixed  with  nebulosity ;  and  Lord  Kosse 
remarks,  that  when  we  turn  the  eye  from  the  telescope 
to  the  Milky  "Way,  the  similarity  is  so  striking,  that  it 
is  impossible  not  to  feel  a  conviction  that  the  nebulosity 
in  both  proceeds  from  the  same  cause. 

The  annular  nebula  in  Lyra  shows  filaments  proceed- 
ing from  the  edge  of  the  ring,  and  also  several  filaments 
partly  filling  up  the  interior  of  the  ring.  By  the  three 
feet  speculum  it  was  not  resolved;  but  the  filaments  be- 
came conspicuous  under  increasing  magnifying  power, 
which  circumstance  is  strikingly  characteristic  of  a  cluster. 

The  nebula  in  the  Dog's  Ear  was  formerly  regarded 


RESOLUTION  OF  KEMAEKABLE  NEBULA.  199 

as  a  representation  of  our  own  Milky  Way,  and  although 
unresolved,  it  was  by  common  consent  considered  a 
mighty  cluster.  At  the  meeting  of  the  British  Associa- 
tion in  1845,  Lord  Rosse  showed  a  sketch  of  its  appear- 
ance as  seen  by  aid  of  his  six  feet  mirror.  The  former 
simple  shape  of  this  nebula  is  transformed  into  a  scroll, 
apparently  unwinding  with  numerous  filaments,  and  a 
mottled  appearance,  which  looks  like  the  breaking  up  of 
a  cluster. 

The  great  nebula  in  Orion  has  been  examined  with 
every  great  telescope  since  the  invention  of  that  instru- 
ment, but  until  recently  without  the  remotest  aspect  of  a 
stellar  constitution.  During  Sir  John  Herschel's  residence 
at  the  Cape  of  Good  Hope,  he  examined  this  nebula 
under  the  most  favorable  circumstances,  when  it  was  near 
the  zenith — but  still  there  was  no  trace  of  a  star,  only 
branches  added  without  number,  so  as  almost  to  obliter- 
ate the  nebula's  previous  form.  During  the  winter  of 
1844-5,  Lord  Rosse  examined  it  with  his  three  feet 
mirror  with  the  utmost  care,  but  without  detecting  the 
vestige  of  a  star.  In  the  winter  of  1845-6,  the  six  feet 
telescope  was  directed,  for  the  first  time,  to  this  wonderful 
object,  and  in  March,  1846,  Lord  Rosse  made  the  follow- 
ing announcement :  "I think  I  may  safely  say  that  there 
can  be  little  if  any  doubt  as  to  the  resolvability  of  this 
nebula.  We  can  plainly  see  that  all  about  the  trapezium 
is  a  mass  of  stars ;  the  rest  of  the  nebula  also  abounding 
with  stars,  and  exhibiting  the  characteristics  of  resolv- 
ability strongly  marked." 


200  HISTOEY  OF  ASTBONOMY. 

Mr.  Bond,  with,  the  great  telescope  at  Cambridge,  has 
also  seen  this  nebula  partially  resolved.  To  him  the  head 
of  the  nebula  appears  composed  of  several  clusters  of 
stars,  the  components  being  separately  seen  for  a  moment 
under  favorable  circumstances. 

Mr.  Lassell  observed  the  nebula  of  Orion  with  his 
twenty  feet  equatorial  at  Malta  under  the  most  favorable 
circumstances.  The  following  are  extracts  from  his 
journal: 

"  1852,  Dec.  6.  Viewed  the  nebula  with  powers  219 ;  260 
and  1018.  With  the  latter  power,  a  new  phase  was  given 
to  the  nebula,  which  seemed  like  large  masses  of  cotton 
wool  packed  one  behind  another ;  the  edges  pulled  out 
so  as  to  be  very  filmy. 

"  Dec.  8.  I  applied  a  power  of  1018,  with  which  there 
is  no  appearance  of  resolvability.  The  whole  aspect  is 
that  of  a  number  of  masses  of  fleecy  cloud,  thin  at  the 
edges,  and  packed  one  behind  another,  appearing  to  be 
a  deep  stratum  of  successive  layers  of  nebulous  sub- 
stance. 

"Dec.  15.  A  few  more  stellar  points,  I  believe,  appear 
than  I  have  mapped  down  in  my  Starfield  diagram,  and 
the  stars  contained  in  those  diagrams  are  very  much 
brighter.  With  power  1018,  the  wool-like  masses  appear 
as  I  have  previously  described  them,  and  there  is  no  dis- 
position whatever  in  them  to  turn  into  stars." 

The  Great  Nebula  in  Andromeda  has  also  been  care- 
fully observed  with  the  Cambridge  telescope.  The  most 
conspicuous  features  were  the  sudden  condensation  of 


RESOLUTION  OF  REMARKABLE  NEBULA.  201 

light  at  the  center  into  an  almost  star-like  nucleus ;  and 
the  vast  number  of  stars  of  every  gradation  of  brilliancy 
scattered  over  its  surface,  which  yet  had  the  undefinable, 
but  still  convincing  aspect  of  not  being  its  components. 
It  is  estimated  that  above  fifteen  hundred  stars  are  visible 
with  the  full  aperture  of  the  object-glass  within  the  limits 
of  the  nebula.  "With  high  powers,  minute  stars  are  dis- 
covered on  the  borders  of  the  nucleus,  but  it  has  thus 
far  yielded  no  evidence  of  resolution.  Minute  descrip- 
tions, accompanied  with  accurate  drawings  of  both  these 
nebulae,  have  been  recently  given  by  the  Messrs.  Bond  in 
the  Memoirs  of  the  American  Academy,  Yol.  HL 

On  the  whole,  it  appears  that  the  increase  in  the  power 
of  our  telescopes  has  added  to  the  number  of  the  clusters 
at  the  expense  of  the  nebulae  properly  so  called ;  still,  as 
Lord  Kosse  has  remarked,  it  would  be  very  unsafe  to 
conclude  that  such  will  always  be  the  case,  and  thence  to 
infer  that  all  nebulosity  is  but  the  glare  of  stars  too  re- 
mote to  be  separated  by  the  utmost  power  of  our  instru- 
ments. While  Lord  Eosse's  telescope  has  shown  certain 
nebulae  to  contain  an  immense  number  of  stars,  it  has 
also  revealed  to  us  new  nebulous  appendages  of  extreme 
faintness,  which  we  must  regard  either  as  not  composed 
of  stars,  or  as  composed  of  stars  of  very  small  absolute 
dimensions. 

9* 


CHAPTER   IV. 

PROGRESS  OF  ASTRONOMY  IN  THE  UNITED  STATES. 


SECTION   I. 

ASTRONOMICAL  OBSERYATORIES  IN  THE  UNITED  STATES. 

IT  is  but  a  few  years  since  practical  astronomy  began 
to  be  cultivated  in  -the  United  States  in  an  efficient  and 
systematic  manner.  Until  recently,  the  instruments  in 
our  possession  were  but .  few  and  small,  and  the  observa- 
tions which  were  made,  seldom  extended  beyond  the  no- 
tice of  the  time  of  a  solar  or  lunar  eclipse,  or  the  meas- 
urement of  a  comet's  distance  from  neighboring  stars  with 
a  sextant. 

The  most  important  astronomical  enterprise  undertaken 
in  this  country,  during  the  last  century,  was  the  observa- 
tion of  the  transit  of  Venus  in  June,  1769.  Upon  the 
observations  of  this  transit  depended  the  more  accurate 
determination  of  the  sun's  parallax;  from  which  is  de- 
duced the  distance  of  the  earth  from  the  sun,  and  thence 
the  absolute  distances  of  all  the  planets.  Only  three 
transits  of  Venus  are  known  to  have  ever  been  seen  by 
any  human  being.  The  first  occurred  in  December,  1639, 


ASTRONOMICAL  OBSERVATORIES.  203 

and  was  seen  by  but  one  individual,  named  Horrocks, 
who  lived  near  Liverpool,  England.  The  next  transit 
occurred  in  June,  1761,  and  was  carefnlly  observed  in 
different  parts  of  the  world,  and  important  conclusions 
were  drawn  from  it  as  to  the  sun's  parallax.  It  was 
known,  however,  that  its  next  recurrence,  which  was  to 
take  place  in  1769,  would  be  under  more  favorable  cir- 
cumstances, and  several  of  the  governments  of  Europe 
sent  astronomers  to  various  parts  of  the  globe  favorably 
situated  for  the  observations.  France  sent  an  astronomer^ 
to  California,  England  sent  astronomers  to  Hudson's  Bay, 
to  Madras,  and  to  the  Island  of  Otaheite,  in  the  South 
Sea.  Several  Kussian  observers  were  stationed  at 
various  points  of  Siberia  and  the  Kussian  empire. 
The  King  of  Denmark  sent  an  astronomer  to  the 
North  Cape,  and  the  King  of  Sweden  sent  an  observer 
to  Finland. 

The  American  Philosophical  Society,  in  January,  1769, 
appointed  a  committee  of  thirteen  to  observe  this  rare 
phenomenon.  The  gentlemen  thus  appointed  were  dis- 
tributed into  three  committees  for  the  purpose  of  making 
observations  at  three  different  places :  viz.,  in  the  city  of 
Philadelphia ;  at  Norriton,  17*miles  northwest  of  Philadel- 
phia ;  and  the  light-house,  near  Cape  Henlopen,  on  Dela- 
ware Bay.  Dr.  Ewing  had  the  principal  direction  of  the 
observatory  in  the  city,  Mr.  Kittenhouse  at  Norriton,  and 
Mr.  O.  Biddle  at  Cape  Henlopen.  Some  money  was  ap- 
propriated by  the  Philosophical  Society  toward  defraying 
the  expenses  of  the  observations ;  but  this  being  found 


204  HISTOEY  OF  ASTEONOMY. 

insufficient,  aid  was  solicited  and  obtained  from  the  As- 
sembly. Temporary  observatories  were  erected,  tolerably 
well  adapted  to  the  purposes  for  which  they  were  design- 
ed. A  reflecting  telescope  with  a  Dollond  micrometer 
was  purchased  in  London  by  Dr.  Franklin,  with  the 
money  voted  by  the  Assembly;  another  of  the  same 
character  was  presented  by  Thomas  Penn,  of  London ; 
and  other  instruments  were  supplied  in  sufficient  num- 
ber. The  observations  at  the  three  stations  were  all 
successful,  and  an  account  of  them  is  given  in  the  first 
volume  of  the  Transactions  of  the  American  Philosophical 
Society. 

For  more  than  half  a  century  after  the  transit  of  Yenus, 
very  little,  if  any,  progress  seemed  to  have  been  made  to- 
ward the  erection  of  a  permanent  observatory,  or  to- 
ward the  procuring  of  large  instruments  such  as  modern 
astronomy  requires.  The  first  direct  proposition  for  the 
establishment  of  an  observatory  was  contained  in  Mr. 
Hassler's  project  for  the  survey  of  the  coast,  submitted  to 
the  Government  through  Mr.  Gallatin,  in  the  year  1807. 
The  proposition  met  with  no  favor.  The  original  law, 
authorizing  the  survey,  passed  without  any  provision  on 
the  subject,  and  the  law  of  1832  expressly  prohibits  such 
an  establishment.  The  late  John  Quincy  Adams,  in  his 
first  annual  message  in  1825,  strongly  urged  this  subject 
upon  the  attention  of  Congress.  After  recommending 
the  establishment  of  a  National  University,  he  said : 

"  Connected  with  the  establishment  of  a  university,  or 
separate  from  it,  might  be  undertaken  the  erection  of  an 


ASTRONOMICAL  OBSERVATORIES.         205 

astronomical  observatory,  with  provision  for  the  support 
of  an  astronomer,  to  be  in  constant  attendance  of  observa- 
tion upon  the  phenomena  of  the  heavens;  and  for  the 
periodical  publication  of  his  observations.  It  is  with  no 
feeling  of  pride,  as  an  American,  that  the  remark  may  be 
made  that,  on  the  comparatively  small  territorial  surface 
of  Europe,  there  are  existing  upward  of  one  hundred  andr 
thirty  of  these  light-houses  of  the  skies ;  while  through-  ; 
out  the  whole  American  hemisphere  there  is  not  one.  If^J 
we  reflect  a  moment  upon  the  discoveries  which,  in  the 
last  four  centuries,  have  been  made  in  the  physical  consti- 
tution of  the  universe  by  the  means  of  these  buildings, 
and  of  observers  stationed  in  them,  shall  we  doubt  of 
their  usefulness  to  every  nation  ?  And  while  scarcely  a 
year  passes  over  our  heads  without  bringing  some  new 
astronomical  discovery  to  light,  which  we  must  fain  re- 
ceive at  second-hand  from  Europe,  are  we  not  cutting 
ourselves  off  from  the  means  of  returning  light  for  light, 
while  we  have  neither  observatory  nor  observer  upon  our 
half  of  the  globe,  and  the  earth  revolves  in  perpetual 
darkness  to  our  unsearching  eyes  ?" 

This  eloquent  appeal  from  the  chief  magistrate  of  the 
country,  in  behalf  of  the  cause  of  science,  was  received 
with  a  general  torrent  of  ridicule ;  and  the  proposition  to 
establish  a  light-house  in  the  skies  became  a  common  by- 
word of  reproach  which  has  scarcely  yet  ceased  to  be  1 
familiar  to  the  lips  of  men  who  glory  in  their  own  shame/ 
So  strong  was  this  feeling  that,  in  the  year  1832,  in  re- 
viving an  act  for  the  continuance  of  the  survey  of  the 


206 


HISTOEY  OF  ASTRONOMY. 


coast,  Congress  was  careful  to  append  the  proviso,  that 
"nothing  in  the  act  should  be  construed  to  authorize  the 
construction  or  maintenance  of  a  permanent  astronomical  ob- 
servatory." 

YALE  COLLEGE  OBSERVATORY. 


A  donation  made  to  Yale  College  by  Mr.  Sheldon  Clark 
is  believed  to  have  contributed  somewhat  toward  that  im- 
pulse which  astronomy  has  recently  received.  In  1828, 
Mr.  Clark  made  a  donation  of  twelve  hundred  dollars  to 
Yale  College  for  the  purchase  of  a  telescope.  The  tele- 
scope was  ordered  from  Dollond,  of  London ;  it  arrived 
in  1830,  and  was  pronounced  by  the  maker  to  be  "  per- 


ASTRONOMICAL  OBSERVATORIES.  207 

feet,  and  such  an  instrument  as  he  was  pleased  to  send  as 
a  specimen  of  his  powers."     This  instrument  has  a  focal  / 
length  of  10  feet,  and  an  aperture  of  5  inches.     The  ob-  / 
ject-glass  is  almost  perfectly  achromatic.      For  objects 
that  require  a  fine  light,  as  the  nebulae  and  smaller  stars, 
this  instrument  exhibits  great  superiority,  and  its  defin- 
ing power  is  equally  good.    It  has  a  variety  of  eye- 
glasses, and  a  spider-line  micrometer  of  the  best  con- 
struction. 

The  style  of  mounting  of  this  telescope  is  not  equal  to 
its  optical  character.  It  has  an  altitude  and  azimuth  move- 
ment without  graduated  circles,  and  is  rolled  about  the 
room  upon  casters.  The  location  of  the  instrument  was 
peculiarly  unfortunate.  It  was  placed  in  the  steeple  of 
one  of  the  college  buildings,  where  the  only  view  afforded 
of  the  heavens  was  through  low  windows  which  effect- 
ually concealed  every  object  as  soon  as  it  attained  an  alti- 
tude of  thirty  degrees  above  the  horizon.  Under  these 
circumstances,  the  telescope  has  proved  less  serviceable 
to  science  than  might  otherwise  have  been  anticipated. 
On  one  occasion,  however,  circumstances  gave  this  tele- 
scope considerable  celebrity.  The  return  of  Halley's^ 
comet,  in  1835,  was  anticipated  with  great  interest.  The 
most  eminent  astronomers  of  Europe  had  carefully  com-  ) 
puted  the  time  of  its  appearance,  and  the  results  of  their 
computations  had  been  spread  before  the  public  in  all  the 
popular  journals.  All  classes  of  the  community  were 
impatiently  watching  to  learn  the  result  of  these  predic- 
tions. The  comet  was  first  observed  in  this  country  by 


208  HISTOKY  OF  ASTRONOMY. 

Professors  Olmsted  and  Loomis,  witla  the  Clark  telescope, 
weeks  before  news  arrived  of  its  having  been  seen  in 
Europe.  This  was  the  occasion  of  bringing  prominently 
before  the  public  the  importance  of  having  large  tele- 
scopes, with  all  the  instruments  necessary  for  nice  astro- 
nomical observations.  It  gave  a  new  impulse  to  a  plan 
which  had  already  been  conceived  of  establishing  a  per- 
manent observatory  at  Cambridge,  upon  a  liberal  scale — 
a  plan,  however,  which  required  the  momentum  of 
another  and  more  splendid  comet  for  its  completion.  It 
kindled  anew  the  astronomical  spirit  of  Philadelphia, 
and  excited  a  desire  for  instruments  superior  to  those 
which  were  then  possessed.  Indeed  the  importance  of 
systematic  astronomical  observations  was  beginning  to  be 
somewhat  generally  felt,  as  well  as  the  necessity  of  su- 
perior instruments  for  this  purpose,  and  many  embryo 
plans  were  formed  for  the  establishment  of  astronomical 
observatories. 

A  transit  instrument  of  five  feet  focal  length  and  four 
inches  aperture  has  recently  been  presented  to  Yale  Col- 
lege by  Mr.  William  Hillhouse,  of  New  Haven ;  but  for 
want  of  a  suitable  building  for  its  reception,  this  instru- 
ment has  not  yet  been  mounted. 

WILLIAMS   COLLEGE   OBSERVATORY. 

The  first  attempt  to  found  a  regular  astronomical  ob- 
servatory in  this  country  was  made  in  connection  with 
Williams  College,  Massachusetts,  by  Professor  Albert 
Hopkins.  In  1836,  Professor  Hopkins  erected  a .  small 


ASTRONOMICAL  OBSERVATORIES. 


209 


building,  consisting  of  a  center  with  two  wings,  the  whole 
being  48  feet  in  length  by  twenty  in  breadth.  The  cen- 
tral apartment  is  surmounted  by  a  revolving  dome  13 
feet  in  diameter,  and  each  wing  has  an  opening  through 
the  roof  for  meridian  instruments.  Under  the  dome  was 
placed  a  Herschelian  telescope  of  10  feet  focus,  mounted 
equatorially.  The  circle  for  right  ascension  was  a  foot  in 
diameter;  the  declination  semicircle  jvas  30  inches  in 


WILLIAMS   COLLEGE  OBSEEVATOBY. 


diameter.  Both  were  made  by  Mr.  Phelps,  of  Troy,  New 
York,  and  read  to  minutes.  In  the  east  wing  has  been 
placed  a  transit  instrument  by  Troughton,  having  a  focal 
length  of  50  inches,  and  an  aperture  of  three  and  a  half 
inches.  In  the  same  room  is  a  compensation  clock  by 
Molineux. 

In  1852  an  achromatic  refracting  telescope,  having  an 
aperture  of  seven  inches,  and  a  focal  length  of  nine  and  a 


210  HISTORY    OF  ASTRONOMY. 

half  feet,  was  presented  to  Williams  College  by  the  late 
Amos  Lawrence,  Esq.,  of  Boston.  The  optical  part  was 
manufactured  by  Mr.  Clark,  of  Boston,  and  the  mounting 
was  furnished  by  Phelps.  The  instrument  is  mounted 
equatorially,  and  has  a  clock  movement.  It  will  afford 
some  indication  of  the  excellence  of  this  instrument  to 
state  that  the  sixth  star  in  the  trapezium  of  Orion  has 
been  seen  by  it.  This  telescope  has  been  mounted  under 
the  dome  of  the  observatory  in  place  of  the  former  re- 
flecting telescope. 

HUDSON  OBSERVATORY,  OHIO. 

The  next  experiment  for  an  observatory  was  made  in 
Ohio,  in  connection  with  the  Western  Beserve  College. 
Having  been  elected  to  the  professorship  of  mathematics 
and  astronomy  in  this  institution  in  the  spring  of  1836, 
the  writer  was  sent  to  Europe  for  the  purchase  of  instru- 
ments and  books,  and  returned  in  the  autumn  of  1837 
with  an  equatorial  telescope,  a  transit  circle,  and  a  clock, 
During  the  next  season  a  building  was  erected,  which, 
though  quite  moderate  in  dimensions,  was  well  suited  to 
the  accommodation  of  the  instruments.  The  entire  length 
of  the  building  is  37  feet,  and  its  breadth  16  feet.  The 
transit  room  is  10  feet  by  12  upon  the  inside,  having  a 
sandstone  pier  in  its  center.  The  pier  is  entirely  detached 
from  the  building,  and  descends  about  six  feet  below  the 
surface  of  the  earth.  The  transit  commands  an  unob- 
structed meridian  from  ninety  degrees  zenith  distance  on 
the  south,  to  eighty-nine  on  the  north. 


ASTRONOMICAL  OBSERVATORIES. 


211 


GBOTTNT)  PL4JS   OF  HT7D80K   OiJBEEVATOBY. 


The  center  room  is  occupied  by  the  equatorial.  It  is 
14  feet  square  on  the  inside,  and  is  surmounted  by  a  re- 
volving dome  of  nine  feet  internal  diameter.  The  equa- 
torial pier  descends  six  feet  below  the  surface  of  the 
ground,  and,  like  the  transit  pier,  has  a  slope  of  one  inch 
4a  the  foot. 


212  HISTOEY  OF  ASTRONOMY. 

The  transit  circle  was  made  by  Simms,  of  London.  It 
has  a  telescope  of  30  inches  focal  length,  with  an  aper- 
ture of  nearly  three  inches.  The  circle  is  18  inches  in 
diameter,  graduated  on  platina  to  five  minutes ;  and  it 
•  has  three  reading  microscopes,  each  measuring  single 
seconds. 

The  equatorial  telescope,  made  also  by  Simms,  has  a 
focal  length  of  five  and  a  half  feet,  with  an  aperture  of 
about  4  inches.  The  hour  circle  is  12  inches  in  diameter, 
graduated  to  single  minutes,  and  reads  by  two  verniers 
to  single  seconds  of  time.  The  declination  circle  is  also 
12  inches  in  diameter,  graduated  to  ten  minutes,  and 
reads  by  two  verniers  to  ten  seconds  of  arc. 

The  clock  was  made  by  Molineux,  and  has  a  mercurial 
pendulum.  The  instruments  were  first  placed  in  the  ob- 
servatory September,  1838,  and  during  the  whole  time 
of  his  residence  in  Ohio,  the  author  pursued  a  systematic 
course  of  observations,  as  far  as  his  engagements  in  the 
college  would  permit,  and  without  the  advantage  of  an 
assistant.  Among  these  observations  may  be  mentioned, 
260  moon  culminations  for  longitude,  69  culminations 
of  Polaris  for  latitude,  16  occultations,  5  comets,  with 
sufficient  accuracy  to  afford  a  determination  of  their 
orbits,  besides  a  great  variety  of  other  objects,  for  reg- 
ulating the  clock,  etc. 

The  moon  culminations  observed  at  Hudson  have  been 
compared  with  European  observations,  as  far  as  corre- 
sponding ones  were  made,  and  the  following  is  the  result : 
On  119  nights  the  moon  was  observed  both  at  Green- 


ASTRONOMICAL  OBSERVATORIES.        213 

wich  and  Hudson ;  on  107  nights  it  was  observed  both  at 
Edinburg  and  Hudson ;  on  95  nights  at  Cambridge  (Eng- 
land) and  Hudson ;  on  88  nights  at  Hamburg  and  Hudson ; 
and  on  40  nights  at  Oxford  and  Hudson.  The  discussion 
of  all  these  observations,  the  results  of  which  are  pub- 
lished in  Gould's  Astronomical  Journal,  has  furnished 
the  longitude  of  Hudson  from  Greenwich  with  a  pre- 
cision such  as  has  been  attained  at  but  few  other  places 
in  the  United  States. 

In  the  summer  of  1849,  the  observatory  at  Hudson 
was  compared  with  that  at  Philadelphia  by  means  of  the 
electric  telegraph,  numerous  signals  having  been  trans- 
mitted to  and  fro  on  four  different  nights,  and  the  differ- 
ence of  longitude  between  these  places  has  thus  been 
settled  within  a  small  fraction  of  a  second.  The  accurate 
determination  of  the  geographical  position  of  a  single 
such  place  in  a  new  State,  affords  a  standard  of  reference 
by  which  a  large  surrounding  territory  is  tolerably  well 
located  through  the  medium  of  the  local  surveys. 

•    PHILADELPHIA  HIGH-SCHOOL  OBSERVATORY. 

The  High-School  observatory  at  Philadelphia  was 
erected  at  about  the  same  time  with  that  of  "Western 
Reserve  College,  but  the  instruments  were  not  received 
until  the  autumn  of  1840.  In  the  year  1837,  a  com- 
mittee was  appointed  by  the  Board  of  Controllers  of 
Public  Schools  on  the  subject  of  establishing  a  Central 
High-School  in  Philadelphia.  At  one  of  the  meetings 
of  the  committee,  Mr.  George  M.  Justice  proposed  the 


214 


HISTOKY  OF  ASTRONOMY. 


PHILADELPHIA  HIGH-SCHOOL   OBSEBVATOEY. 


erection  of  an  observatory  to  be  attached  to  the  school, 
and  that  the  use  of  astronomical  instruments  should  be 
taught  as  a  regular  branch  of  study.  The  committee 
unanimously  adopted  the  suggestion,  and  placed  the 
erection  of  the  observatory  and  furnishing  the  instru- 
ments under  the  care  of  Mr.  Justice.  The  Controllers 
placed  at  the  disposal  of  the  committee  the  sum  of  $5000 
to  furnish  the  observatory.  In  accordance  with  the  ad- 
vice of  Mr.  Sears  C.  "Walker,  it  was  decided  to  order  the  in- 
struments from  Munich,  in  preference  to  London  or  Paris. 


ASTRONOMICAL  OBSERVATORIES.  215 

In  the  year  1838  a  tower,  about  45  feet  high,  was 
erected  in  the  rear  of  the  school  building,  and  was  in- 
sulated 10  feet  below  the  surface  of  the  earth.  The  brick 
walls  were  three  feet  thick  at  bottom,  and  two  and  a  half 
feet  thick  at  top,  and  the  diameter  of  the  tower  was 
about  12  feet  in  the  clear.  It  was  surmounted  by  a 
dome  18  feet  in  diameter,  weighing  about  two  tons.  The 
telescope  rested  on  two  marble  slabs,  each  weighing  about 
a  thousand  pounds,  which  were  supported  by  two  strong 
cast-iron  beams  that  reached  from  the  north  to  the  south 
brick  wall,  and  thus  bound  the  two  walls  together. 

The  equatorial,  by  Merz  and  Mahler,  of  Munich,  is  of 
eight  feet  focal  length,  and  six  inches  aperture,  with 
clock-work  movement.  The  hour  circle  is  nine  inches 
in  diameter,  reading  to  four  seconds  of  time ;  the  declina- 
tion circle  is  12  inches  in  diameter,  reading  to  ten  seconds 
of  arc.  This  telescope  is  mounted  like  the  celebrated 
telescope  at  Dorpat,  and  has  a  variety  of  powers  to  480, 
with  micrometers. 

The  meridian  circle  is  by  Ertel,  of  Munich,  and  was 
mounted  on  marble  pillars  resting  on  the  south  wall  of 
the  tower.  The  telescope  has  an  object-glass  of  five 
feet  focal  length,  four  and  a  half  inches  aperture,  and  is 
so  constructed  that  the  object-glass  and  eye-glass  may 
be  made  to  change  places.  It  has  two  circles,  each 
graduated  to  read  by  the  aid  of  four  verniers  to  two 
seconds  of  arc.  The  clock  is  by  Lukens,  and  has  a  mer- 
curial pendulum.  The  cost  of  the  several  instruments 
was  as  follows:  equatorial  telescope,  $2,200;  meridian 


216 


HISTOEY  OF  ASTRONOMY. 


PHILADELPHIA  KQXTATOBIAL. 

circle,  $1,200 ;   clock,  $300 ;   comet  seeker,  $245 ;  chro- 
nometer, $250. 

The  erection  of  this  observatory  formed  an  epoch  in 
the  history  of  American  astronomy,  in  consequence  of 
the  introduction  of  a  class  of  instruments  superior  to  any 


ASTRONOMICAL  OBSERVATORIES.  217 

• 

which  had  been  hitherto  imported.  It  introduced  the 
instruments  of  Munich  fairly  to  the  notice  of  the  Ameri- 
can public ;  and  their  superiority  to  the  English  telescopes 
was  felt  to  be  so  decided,  that  almost  every  large  instru- 
ment which  has  been  since  imported  has  been  from  the 
same  makers.  In  the  hands  of  Messrs.  Walker  and 
Kendall,  this  observatory  became  celebrated,  not  only  in 
America,  but  also  in  Europe.  It  has  furnished  436  moon 
culminations,  about  120  occupations  of  stars,  and  several 
series  of  observations  for  latitude  ;  together  with  numer- 
ous observations  of  comets,  especially  the  great  comet  of 
1843.  This  was  also  an  important  station  in  several  of 
the  earlier  telegraph  operations  for  longitude. 

The  ground  occupied  by  the  High  School  being  needed 
for  the  accommodation  of  one  of  the  railroads  leading  out 
of  the  city,  the  building  and  lot  were  sold  in  1853,  and  a 
new  lot  was  purchased  on  Broad-street,  about  250  rods 
north  from  the  former  site.  Here  a  new  school  building 
and  observatory  have  been  erected,  and  the  instruments 
were  set  up  in  the  autumn  of  1854.  The  following  is  a 
description  of  the  new  observatory  : 

For  the  support  of  the  instruments,  two  parallel  piers 
of  solid  masonry,  nearly  at  right  angles  to  the  plane  of 
the  meridian,  each  16  feet  wide  and  2J  feet  thick,  were 
erected  in  the  central  front  part  of  the  building.  They 
are  18  feet  apart,  being  separated  by  the  main  entrance - 
hall  and  principal  stairway ;  the  latter  extending  to  the 
fourth  story  of  the  tower.  The  piers  are  inclosed  and 
completely  isolated,  and  extend  from  below  the  founda- 

10 


218  HISTORY  OF  ASTRONOMY. 

tions  of  the  building  to  a  height  of  90  feet,  terminating 
about  one  foot  above  the  ceiling  of  the  fourth  story  of  the 
tower.  They  are  tied  together  at  each  floor  by  wooden 
beams,  and  at  the  top  by  four  cast-iron  girders — a  pair, 
four  and  a  half  feet  apart,  being  placed  near  each  end. . 

The  observing  room  is  24  feet  square,  and  is  covered 
by  a  flat  roof  with  the  exception  of  the  part  occupied  by 
the  equatorial. 

The  eastern  pair  of  iron  girders  are  framed  together 
midway  between  the  piers,  and  upon  this  frame-work  is, 
constructed  of  bricks  and  cement,  a  prism,  four  feet 
square  at  the  base,  reaching  nearly  to  the  floor,  and  from 
this  point  a  cylinder,  three  feet  in  diameter,  rises  three 
feet  above  the  floor.  This  cylinder  is  incased  in  a  drum 
of  boiler  iron.  The  marble  stand  of  the  telescope  is  im- 
bedded to  a  depth  of  18  inches  in  the  cylinder,  and  rises 
to  a  height  of  six  feet  and  three  quarters  above  it.  The 
equatorial  is  covered  by  a  hemispherical  dome  of  12  feet 
in  diameter,  constructed  upon  the  plan  of  that  of  Mr. 
Campbell's  observatory  in  New  York,  with  revolving 
table  and  steps  attached.  To  secure  a  firm  support  for 
the  dome,  a  frame-work  of  cast  iron  is  constructed  below 
the  floor,  resting  on  the  walls  within  the  piers.  From 
this  frame-work,  eight  equidistant  cast-iron  columns  ex- 
tend to  the  ceiling,  and  upon  these  a  substantial  ring, 
12  feet  in  diameter,  composed  of  wood  and  iron,  serves 
as  the  foundation  for  the  plate  upon  which  the  dome  re- 
volves. 

The  western  end  of  the  southern  pier  is  extended  to 


ASTRONOMICAL  OBSERVATORIES.         219 

within  about  one  foot  of  the  floor,  and  is  capped  by  a 
slab  of  marble,  eight  inches  thick,  upon  which  the  piers 
of  the  transit  circle  stand.  In .  the  direction  of  the  meri- 
dian of  the  transit  is  a  clear  opening,  26  inches  wide,  in 
the  roof  and  down  the  sides  to  within  about  two  feet  of 
the  floor.  On  each  side  of  the  transit  circle  a  flexible  gas 
tube  hangs  from  the  ceiling.  One  light  is  used  to  illumi- 
nate the  wires  of  the  transit,  while  the  other  is  used  in 
reading  the  circle. 

The  clock  is  attached  to  the  western  wall,  near  the 
transit  instrument,  and  is  lighted  by  gas. 

Adjoining  the  observing  room  on  the  east,  is  a  small 
apartment  which  serves  as  a  library  and  computing  room. 
This  room  is  provided  with  a  stove,  for  which  reason  the 
two  rooms  do  not  communicate  directly  with  each  other, 
but  both  open  on  the  staircase  leading  from  the  fourth 
story  to  the  observatory. 

WEST  POINT  OBSERVATORY. 

The  "West  Point  observatory  was  erected  about  the 
same  time  with  that  at  Philadelphia.  In  1839,  a  large 
building  was  erected  for  the  accommodation  of  the  library 
and  philosophical  apparatus,  with  three  towers  for  the  re- 
ception of  astronomical  instruments.  The  central  tower 
is  surmounted  by  a  traveling  dome,  27  feet  in  diameter, 
and  about  17  feet  high  from  the  spring.  It  is  pierced  by 
five  window-openings  near  the  curb,  and  an  observing 
slit,  two  feet  wide,  extending  from  a  point  four  feet  above 
the  floor  to  nearly  two  feet  on  the  opposite  side  of  the 


ASTRONOMICAL   OBSERVATORIES. 


221 


zenith.  The  dome  rests  on  six  twenty-four  pound  can- 
non-balls, which  turn  between  two  cast-iron  annular 
grooves. 


In  the  two  flank  towers,  meridian  observing  slits  are 
made,  about  20  inches  in  the  clear.  These  begin  about 
two  and  a  half  feet  from  the  floor,  and  extend  through 


222  HISTOKY  OF  ASTRONOMY. 

the  roof,  thus  affording  an  uninterrupted  view  of  the 
celestial  meridian  from  the  southern  to  the  northern 
horizon. 

- 

f      In  the  year  1840,  Professor  Bartlett  visited  the  prin- 
/     cipal  observatories  in  England,  Scotland,  Ireland,  France, 
Belgium,  and  Bavaria,  and  ordered  three  large  instru- 
ments, viz.,  an  equatorial  telescope,  a  transit  instrument, 
Vv    and  a  mural  circle. 

The  equatorial,  which  was  erected  in  the  central  tower, 
was  mounted  by  Mr.  Thomas  Grubb,  of  Dublin.  The 
telescope,  made  by  Lerebours,  of  Paris,  is  a  refractor  of 
eight  feet  focal  length,  and  six  inches  aperture.  It  has  a 
position  micrometer,  furnished  with  an  illuminating  ap- 
paratus for  bright  lines  and  dark  field.  The  telescope  is 
moved  by  clock-work,  so  that  the  object  under  ex- 
amination is  easily  kept  in  the  center  of  the  field  of 
view. 

In  the  east  tower  is  a  transit  telescope,  by  Ertel.  and 
Son,  of  Munich.  It  has  a  clear  aperture  of  five  and  a 
quarter  inches,  with  a  focal  length  of  seven  feet,  and  is 
supplied  with  all  the  appendages  necessary  to  facilitate 
the  making  of  observations.  There  is  in  this  tower  a  fine 
sidereal  clock,  by  Hardy. 

In  the  west  tower  is  a  mural  circle,  by  Simms,  of  Lon- 
don. It  is  cast  in  one  entire  piece  of  brass,  instead  of 
the  old  mode  of  frame-work.  Its  diameter  is  five  feet, 
and  the  graduations  are  upon  two  bands,  one  of  gold  the 
other  of  palladium.  The  telescope  has  a  clear  aperture 
of  four  inches,  and  a  focal  length  of  five  feet.  It  is  pro- 


ASTRONOMICAL  OBSERVATORIES.  223 

vided  with  all  the  usual  means  of  adjustment,  together 
with  a  vertical  collimating  eye-piece,  and  an  illuminating 
apparatus  for  dark  field  and  bright  lines.  Professor 
Bartlett,  the  director  of  the  observatory,  has  suEjecited 
this  instrument  to  a  severe  trial,  and  finds  the  probable 
error  in  the  measurement  of  an  angle  of  60°  to  be  but 
0".22,  exclusive  of  the  error  of  reading.  There  is  also  a 
sidereal  clock  in  the  same  tower. 

A  new  refracting  telescope,  designed  to  take  the  place 
of  the  Grubb  telescope  in  the  central  tower  of  this  ob- 
servatory, has  just  been  completed  by  Mr.  Henry  Fitz. 
This  telescope  has  a  focal  length  of  14  feet,  and  an  aper- 
ture of  nine  and  three  fourths  inches.  It  has  seven  neg- 
ative and  six  positive  eye-pieces,  the  highest  magnifying 
power  being  1000.  The  circles  are  each  20  inches  in 
diameter,  the  hour  circle  reading  to  two  seconds  of  time, 
and  the  declination  circle  to  20  seconds  of  arc.  The  price 
of  this  telescope  was  $5000. 

Professor  Bartlett  made  a  series  of  observations  on  the 
great  comet  of  1843,  which  are  published  in  the  "  Trans- 
actions of  the  American  Philosophical  Society."  He  has 

also  made  numerous  observations  with  the  meridional  in- 

. 

struments,  which  have  not  yet  been  published. 

NATIONAL  OBSERVATORY  AT  "WASHINGTON 

Soon  after  the  completion  of  the  West  Point  observa- 
tory, the  National  observatory  at  Washington  was  com- 
menced. The  origin  of  this  establishment  may  be  traced 
to  the  wants  of  the  naval  service.  In  the  year  1831,  there 


224 


HISTORY  OF  ASTRONOMY. 


was  established  at  Washington  a  depot  of  charts  and  in- 
struments for  the  use  of  the  navy.  A  small  transit  in- 
strument was  erected  in  a  small  wooden  building  near  the 
Capitol,  and  used  for  the  rating  of  chronometers.  This 
d£pot  was  for  several  years  under  the  superintendence  of 
Lieutenant  (now  Captain)  Wilkes.  When,  in  1838,  this 
officer  took  command  of  the  exploring  expedition,  he  rec- 
ommended that  a  series  of  observations  should  be  made 


NATIONAL  OJ3BEBVATORY  AT  WASHINGTON. 


in  this  country,  during  his  absence,  upon  such  celestial 
phenomena  as  might  be  available  for  the  better  determi- 
nation of  his  longitudes,  and  their  reference  to  some 
meridian  at  home.  The  government  sanctioned  the  rec- 
ommendation, and  the  observations  were  directed  to  be 
made  at  Dorchester  by  Mr.  Bond,  and  at  Washington  by 
Lieutenant  Gilliss.  This  series  was  continued  until  the 
return  of  the  expedition,  in  1842. 


ASTRONOMICAL  OBSERVATORIES.  225 

On  his  return  from  Europe,  in  1840,  Professor  Bartlett\ 
made  a  report  to  the  Engineer  Department  at  Washing- 
ton on  the  observatories  of  Europe.  In  this  report  he 
embodied  the  modern  improvements  in  the  construction 
of  instruments,  as  -well  as  the  erection  of  observatories. 
He  afterward  prepared  a  plan  and  estimates  for  an  ob- 
servatory at  Washington,  for  Mr.  Poinsett,  then  Secretary 
of  War. 

In  1842  was  passed  an  Act  of  Congress  authorizing  the 
erection  of  a  depot  of  charts  and  instruments  for  the  navy, 
the  expense  being  limited  to  $25,000.  Lieutenant  Gilliss 
was  instructed  by  the  Secretary  of  the  Navy  to  present  a 
plan  of  a  building,  after  consultation  with  the  principal 
astronomers  of  the  United  States.  The  plan  thus  pre- 
pared was  afterward  submitted  to  the  most  eminent  as- 
tronomers of  Europe,  and  the  model  finally  adopted  em- 
braced such  improvements  as  they  had  recommended. 
The  observatory  consists  of  a  central  building  of  brick, 
with  wings  upon  the  east,  west,  and  south  sides.  The 
central  building  is  50  feet  square,  two  stories  high,  with 
a  basement,  and  is  surmounted  by  a  revolving  dome  23 
feet  in  diameter,  with  an  elevation  of  18  feet  from  the 
floor.  Directly  under  the  dome  is  the  great  pier,  whose 
diameter  at  the  base  is  15  feet,  and  tapers  gradually  to 
the  top,  upon  which  rests  the  great  equatorial.  The  cen- 
tral building,  except  the  dome,  is  employed  exclusively 
for  official  purposes.  The  west  wing  is  21  by  26  feet, 
and  18  feet  high,  and  is  appropriated  to  the  meridian 
transit  instrument.  The  east  wing  is  48  by  21  feet,  and 

10* 


226 


HISTOEY  OF  ASTKONOMY. 


is  divided  into  two  rooms,  in  one  of  which  are  the  mural 
circle  and  the  meridian  circle,  and  in  the  other  are  the 
chronometers.  The  wing  on  the  south  side  is  21  by  40 


feet,  in  two  apartments.  In  the  first  apartment  is  the 
transit  in  the  prime  vertical,  and  in  the  second  apartment 
is  the  new  refraction  circle.  In  each  of  these  wings  is 


ASTRONOMIC^  OBSERVATORIES.  227 

a  clock  regulated  to  sidereal  time.  Immediately  east  of 
the  observatory  is  the  dwelling  of  the  superintendent. 

The  great  refracting  telescope  was  made  by  Merz  and 
Mahler,  of  Munich.  The  object-glass  has  a  focal  length 
of  15  feet,  and  an  aperture  of  nine  and  a  half  inches. 
This  telescope  is  equatorially  mounted,  and  furnished 
with  clock-work.  It  has  a  repeating  filar  micrometer, 
with  eight  eye-pieces,  magnifying  from  100  to  1000  times. 
The  cost  of  this  telescope  was  $6000,  its  object-glass 
alone  being  valued  at  $3,600. 

The  transit  instrument  has  an  object-glass  with  a  clear 
aperture  of  five  and  a  half  inches,  and  a  focal  length  of 
88  inches,  furnished  by  Merz  and  Mahler,  and  the  in- 
strument was  constructed  by  Ertel  and  Son,  of  Munich. 
It  is  mounted  upon  large  piers  of  granite,  which  rest 
firmly  on  a  foundation  of  stone,  extending  ten  feet  below 
the  surface  of  the  ground.  The  cost  of  this  instrument 
was  $1480 ;  the  object-glass  alone  cost  $320. 

The  mural  circle  was  made  by  Mr.  William  Simms,  of 
London.  It  is  five  feet  in  diameter,  made  of  brass,  and 
cast  in  a  single  piece.  It  is  divided  into  spaces  of  five 
minutes  each,  upon  a  band  of  gold  inlaid  on  the  rim,  or 
perpendicular  to  the  plane  of  the  circle.  Placed  at  equal 
distances  round  the  circle  are  six  micrometer  microscopes, 
with  an  acute  cross  of  wires  at  their  foci,  for  reading 
angles  less  than,  five  minutes.  Five  revolutions  of,  the 
micrometer  are  designed  to  measure  five  minutes  upon 
the  circle.  The  micrometer  heads  being  divided  into 
sixty  equal  parts,  each  division  represents  one  second  of 


228 


HISTORY    OF  ASTRONOMY. 


TBANSIT  INSTRUMENT. 


arc.  The  object-glass  of  the  telescope  has  a  clear  aper- 
ture of  four  inches,  and  a  focal  length  of  five  feet.  At 
its  focus  is  a  fixed  diaphragm,  containing  seven  vertical 


ASTRONOMICAL  OBSERVATORIES.  229 

wires  and  one  horizontal  wire.  There  is  also  another 
diaphragm,  movable  by  a  micrometer  screw,  and  fur- 
nished with  five  horizontal  and  equidistant  wires,  by 
which  the  distance  of  any  star  from  the  fixed  horizontal 
wire  is  measured  as  it  passes  through  the  field.  The 
magnifying  power  ordinarily  employed  is  125.  The  cost 
of  the  mural  circle  was  $3,550. 

The  meridian  circle  was  made  by  Ertel  and  Son,  of 
Munich.  Its  object-glass  has  an  aperture  of  four  and  a 
half  inches,  with  a  focal  distance  of  58  inches.  This 
instrument  is  provided  with  a  circle  30  inches  in 
diameter,  divided  into  arcs  of  three  minutes,  and  reads 
by  four,  microscopes  to  single  seconds.  The  clock  in  the 
east  wing  has  a  mercurial  pendulum,  and  was  made  by 
Charles  Frodsham. 

The  transit  in  the  prime  vertical  was  made  by  Pistor 
and  Martins,  of  Berlin.  The  object-glass  of  the  telescope 
has  a  clear  aperture  of  five  inches,  with  a  focal  length 
of  78  inches.  The  eye-tube  carries  a  system  of  2  hori- 
zontal and  15  vertical  stationary  wires,  with  one  movable 
vertical  wire.  This  instrument  is  mounted  at  one  end 
of  its  axis  and  outside  of  its  supports.  It  is  reversed 
from  one  side  to  the  other  twice  during  every  observa- 
tion; and  though  it  weighs  upwards  of  1000  pounds, 
so  perfect  is  its  system  of  counterpoises  and  the  reversing 
apparatus,  that  a  child  can  lift  it  from  its  supports,  reverse 
and  replace  it  in  them,  in  less  than  one  minute.  The 
cost  of  this  instrument  was  $1750.  The  clock  in  this 


230 


HISTORY  OP  ASTRONOMY. 


wing  has  a  gridiron  pendulum,  and  was  made  by  Charles 
Frodsham. 


PBIME  VEBTIOAL  TEAN8IT. 


The  refraction  circle  was  made  by  Ertel  and  Son,  from 
plans  and  drawings  furnished  by  Lieutenant  Maury.  The 
telescope  is  eight  and  a  half  feet  in  length,  with  a  clear 
aperture  of  seven  inches.  It  is  supported  in  the  middle 
of  the  axis  between  two  piers,  and  it  has  two  circles  of 


ASTRONOMICAL  OBSERVATORIES.  231 

four  feet  diameter,  one  on  each  end  of  the  axis,  divided 
on  gold  into  arcs  of  two  minutes.  Each  circle  is  pro- 
vided with  six  reading  microscopes.  The  telescope  has 
two  micrometers,  one  moving  in  azimuth,  the  other  in 
altitude. 

The  comet-seeker  was  made  by  Merz  and  Mahler. 
It  has  an  object-glass  of  about  4  inches  in  diameter, 
and  with  a  focal  length  of  32  inches,  with  which  low 
magnifying  powers  are  used,  that  it  may  embrace  a  large 
field,  and  collect  the  greatest  possible  quantity  of  light. 
The  cost  of  this  instrument  was  $280. 

In  the  fell  of  1844,  Lieutenant  Maury  was  directed  to 
take  charge  of  the  new  "Depot  of  Charts  and  Instru- 
ments." Lieutenant  Maury  commenced  a  regular  and 
systematic  series  of  observations  upon  the  sun  and  moon, 
the  planets,  and  a  list  of  fundamental  stars,  comprising 
those  of  the  greatest  magnitude  and  of  the  most  favorable 
positions,  to  be  used  as  standard  stars.  He  also  under- 
took observations  for  a  most  extensive  catalogue  of  stars. 

This  work  contemplates  a  regular  and  systematic  ex- 
amination of  every  point  of  space  in  the  heavens  that  is 
visible  at  Washington,  and  of  assigning  position,  color, 
and  magnitude  to  every  star  that  the  instruments  are 
capable  of  reaching.  The  following  plan  of  sweeping 
was  adopted :  The  telescope  of  the  mural  circle  is  set 
in  altitude,  and  all  the  microscopes  carefully  read  and 
recorded,  and  the  eye-piece  is  moved  up  and  down  so 
as  to  cover  a  belt  of  about  50  minutes  in  declination. 
The  micrometer  diaphragm  is  provided  with  a  number 


232  HISTOKY  OF  ASTRONOMY. 

of  parallel  wires,  the  intervals  of  which  have  been  care- 
fully determined.  Thus,  in  whatever  part  of  the  field  a 
star  appears,  a  micrometer  wire  is  close  at  hand,  and  the 
star  is  bisected  by  the  nearest  wire,  while  the  time  at 
which  it  passes  the  several  vertical  wires  is  also  noted. 
The  number  of  the  bisecting  wire,  and  the  reading  of  the 
micrometer  being  now  entered,  the  observation  is  complete. 

The  observer  thus  keeps  his  eye  at  the  telescope  for 
hours  at  a  time,  and,  under  favorable  circumstances,  can 
observe  with  ease  two  or  three  hundred  stars  during  the 
night.  The  transit  instrument,  by  means  of  a  mi- 
crometer moving  in  altitude,  is  converted  into  a  difference 
of  declination  instrument,  and  occupies  the  adjoining  belt 
above  the  mural,  the  two  instruments  being  so  set  that 
ten  minutes  of  declination  are  common  to  the  field  of 
both.  The  meridian  circle  in  the  same  way  occupies  the 
belt  below  the  mural.  The  next  night  the  instruments 
change  places,  and  go  over.. the  same  ground,  i.  e.t  the 
meridian  circle  covers  the  same  belt  to-night  which  on 
the  former  night  was  swept  by  the  mural.  The  two  lists 
are  immediately  compared,  and  should  it  appear  that  any 
of  the  stars  have  changed  their  position,  the  large  equa- 
torial is  put  in  pursuit,  to  see  whether  they  are  fixed 
stars  or  not. 

This  great  work  contemplates  the  examination  of  every 
star  down  to  the  tenth  magnitude  in  the  entire  visible 
heavens ;  and  while  it  looks  to  the  discovery  of  new 
planets  and  unknown  stars,  it  also  aims  to  detect  the  dis- 
appearance of  any  stars  found  in  existing  catalogues. 


ASTRONOMICAL  OBSERVATORIES.  233 

In  December,  1849,  the  use  of  the  electric  clock  was 
introduced  at  the  Washington  observatory,  and  the 
original  method  of  observation  was  somewhat  modified. 
In  the  west  transit  instrument  was  inserted  a  new  dia- 
phragm, having  two  systems  of  wires  which  included  75 
spider-lines,  viz.,  one  system  of  vertical  and  one  system 
of  inclined  wires.  Each  system  is  divided  into  groups 
of  five  wires  each.  By  observing  the  transit  •  of  a  star 
over  a  group  of  vertical  wires,  its  right  ascension  is  de- 
termined ;  and  by  observing  its  transit  over  a  group  of 
inclined  wires,  the  difference  of  declination  between  this 
and  other  stars  similarly  observed  may  be  computed.  All 
these  observations  are  recorded  on  a  fillet  of  paper  by 
means  of  an  electric  circuit,  by  simply  pressing  a  key 
as  the  star  is  seen  to  pass  each  of  the  wires  of  the  transit 
instrument. 

Three  quarto  volumes  of  Washington  observations  have 
been  published,  viz.,  the  observations  for  1845,  1846, 
and  1847. 

The  volume  for  1845  contains  550  pages,  and  ftirnishes 
a  full  description  of  the  instruments  employed,  illustrated 
by  numerous  engravings.  It  also  famishes  a  large  num- 
ber of  observations  with  the  transit  instrument,  the 
mural  circle,  and  the  prime  vertical  transit.  The  volume 
for  1846  contains  676  pages,  and  besides  observations, 
with  the  instruments  used  in  1845,  furnishes  also  ob- 
servations with  the  meridian  circle  and  equatorial.  All 
these  observation  are  .carefully  reduced,  and  the  places 
of  the  sun,  moon  and  planets,  are  compared  with  their 


234:  HISTORY  OF  ASTRONOMY. 

predicted  places  as  given  in  the  Nautical  Almanac.  The 
volume  for  1847  contains  480  pages,  and  in  its  arrange- 
ment is  similar  to  the  preceding  volume.  These  volumes 
have  placed  our  National  observatory  in  the  first  rank 
with  the  oldest  and  best  institutions  of  the  same  kind  in 
Europe.  But  few  observatories  in  Europe  produce  an 
equal  amount  of  work  in  a  year,  and  in  point  of  ac- 
curacy the  observations  compare  well  with  those  of 
foreign  institutions.  It  is  expected  that  the  volume  for 
1848  will  be  ready  for  the  printer  some  time  during  the 
present  year,  and  that  the  succeeding  volumes  will  fol- 
low with  but  little  delay. 

The  observations  for  the  star  catalogue  have  not  yet 
been  published.  The  number  of  stars  already  observed 
is  estimated  at  about  100,000,  included  between  16  and 
45  degrees  of  south  declination.  The  want  of  sufficient 
force  for  reducing  the  observations  has  caused  the  delay 
in  their  publication. 

During  the  first  two  or  three  years  of  the  operations 
of  the  observatory,  Lieutenant  Maury  devoted  consider- 
able time  to  observations,  especially  with  the  prime  ver- 
tical transit  and  equatorial ;   but  for  several  years  his 
time  has  been  entirely  engrossed  by  general  superintend- 
ence, and  he  has  been  obliged  to  leave  the  observations 
//  to  his  assistants.    It  has  been  customary  to  assign  a  lieu- 
|  tenant  and  a  professor  of  mathematics  to  each  meridional 
^instrument.     Frequent  changes  have  been  made  in  the 
lieutenants  employed  at  the   observatory;    one  set  of 
officers  being  ordered  to  sea,  and  another  set  being  sent 


ASTRONOMICAL  OBSERVATOEIES.  235 

to  supply  their  place.  But  the  professors  of  mathemat- 
ics have  continued  with  tolerable  permanence,  and  have 
acquired  a  corresponding  familiarity  with  the  instru- 
ments, and  the  computations  growing  out  of  their  use. 
The  following  notices  contain  the  names  of  those  who 
have  contributed  most  to  give  character  to  the  ob- 
servatory. 

Professor  John  H.  C.  Coffin  graduated  at  Bowdoin 
College  in  1834,  and  commenced  duty  at-  the  observa- 
tory in  January,  1845.  He  was  immediately  placed  in 
charge  of -the  mural  circle,  and  devoted  his  time  ex- 
clusively to  that  instrument  until  1851,  when  his  eyes 
began  to  suffer  from  the  severe  usage  to  which  they  had 
been  subjected,  and  he  made  but  few  observations  after 
that  time.  In  1853  he  was  detached  from  the  observa- 
tory, and  ordered  to  join  the  Naval  Academy  at  Annap- 
olis, where  he  is  now  employed  in  the  department  of 
instruction.  Professor  Coffin  applied  himself  to  his 
duties  as  an  observer  with  indefatigable  perseverance  ; 
and  the  published  volumes  of  the  Washington  observa- 
tions sufficiently  attest  the  amount  and  value  of  his 
labors. 

Professor  Joseph  S.  Hubbard  graduated  at  Yale  Col- 
lege in  1843,  and  commenced  duty  at  the  observatory  in 
May,  1845.  During  the  first  year  he  had  charge  of  ob- 
servations with  the  transit  instrument ;  in  1846  he  was 
assigned  to  the  meridian  circle ;  in  1847  he  was  trans- 
ferred to  the  equatorial ;  and  since  that  time  he  has  had 
charge  of  the  prime  vertical  transit.  Since  1850  he  has 


236  HISTORY  OF  ASTRONOMY. 

been  chiefly  employed  in  the  reduction  of  back  observa- 
tions. In  1852  and  1853  he  undertook  a  series  of 
observations  on  Alpha  Lyrae  for  the  determination  of 
its  parallax,  but  the  unfavorable  state  of  the  weather 
during  the  month  of  December,  when  the  maximum  of 
parallax  occurs,  frustrated  his  expectations,  and  he  was 
compelled  to  abandon  the  attempt.  Professor  Hubbard 
has  contributed  to  the  Astronomical  Journal  various 
papers  which  have  secured  him  a  high  reputation  among 
astronomers.  Among  these  papers  may  be  mentioned 
his  researches  on  the  great  comet  of  1843 ;  on  the  orbit 
of  Biela's  comet ;  on  the  orbit  of  the  planet  Egeria,  etc. 

Professor  Eeuel  Keith  graduated  at  Middlebury  Col- 
lege in  1845,  and  commenced  duty  at  the  observatory  in 
August  of  the  same  year.  He  was  immediately  assigned 
to  the  meridian  transit,  and  up  to  the  present  time  has 
given  his  exclusive  attention  to  that  instrument.  The 
published  volumes  of  the  observations  show  the  fidelity 
with  which  he  has  discharged  the  duties  assigned  to 
him. 

Professor  Sears  C.  Walker  graduated  at  Harvard  Uni- 
versity in  1825,  and  was  attached  to  the  observatory 
during  the  principal  part  of  the  year  1846.  During 
this  time  he  was  mainly  employed  in  computations 
respecting  the  planet  Neptune ;  in  the  discussion  of  the 
latitude  of  the  observatory;  in  determining  the  error 
of  standard  thermometers,  etc. 

Professor  James  Ferguson,  for  many  years  first  assistant 
in  the  department  of  the  Coast  Survey,  became  connected 


ASTRONOMICAL   OBSERVATORIES. 


237 


with  the  observatory  in  1848,  and  was  immediately  as- 
signed to  the  equatorial,  of  which  he  has  had  sole  charge 
to  the  present  time.  He  has  made  numerous  observations 
of  comets,  and  of  the  small  planets,  and  has  had  the  good 
fortune  to  discover  a  new  asteroid,  Euphrosyne,  being 
the  only  instance  in  which  a  primary  planet  has  been 
first  discovered  bv  an  American  observer. 


GEORGETOWN   OBSERVATORY. 


The  erection  of  the  Georgetown  observatory  was  nearly 
cotemporaneous  with  that  of  the  National  observatory. 
In  December,  1841,  Rev.  -T.  M.  Jenkins  offered  a  dona- 
tion to  the  college  at  Georgetown  for.  the  purpose  of 
building  and  furnishing  an  observatory  ;  and  Rev;  C.  H. 
Stonestreet  offered  to  supply  an  equatorial.  In  1842  the 
donations  were  accepted.  In  the  summer  of  1843  the 


238 


HISTORY  OF  ASTRONOMY. 


foundations  of  the  building  were  laid,  and  it  was  fin- 
ished in  the  spring  of  1844. 

The  ground  on  which  the  observatory  is  built  is  154 
feet  above  the  level  of  the  Potomac  river,  from  which 
it  is  distant  about  half  a  mile.  The  central  part  of  the 
building  is  30  feet  square  on  the  outside,  with  connecting 
wings  both  on  the  east  and  west  sides,  each  of  them 
being  27  feet  by  15,  making  the  entire  length  of  the 
observatory  60  feet.  The  central  part  is  surmounted  by 
a  rotary  dome  20  feet  in  diameter,  which  works  on 
cast-iron  rollers,  8  inches  in  diameter.  The  opening  in 


GEOBQETOWN  OBBEBVATOEY,   SOTJTH  ELEVATION. 

fl 

the  dome  is  2  feet  wide,  and  is  closed  by  4  shutters. 
From  the  cellar,  through  all  the  floors  of  this  part  of 
the  building,  rises  a  pier  of  masonry  41  feet  high.  This 
pier  is  11  feet  square  at  the  base,  and  6  feet  square  at 


ASTRONOMICAL  OBSERVATORIES.  239 

the  top,  and  upon  it  rests  the  equatorial  telescope,  made 
by  Simms,  of  London,  which  was  received  in  1849.  The 
object-glass  has  a  focal  length  of  80  inches,  and  an 
aperture  of  nearly  5  inches,  with  powers,  from  25  to  408. 
The  hour  circle  is  16  inches  in  diameter,  and  reads  to 
one  second  of  time ;  the  declination  circle  is  20  inches 
in  diameter,  and  reads  to  five  seconds  of  arc.  The  -in- 
strument is  supplied  with  clock-work,  by  which  a  celestial 
object  may  be  kept  continually  in  the  field  of  view.  This 
instrument  cost  $2000. 

The  east  and  west  rooms,  which  contain  the  meridian 
instruments,  have  meridian  openings  two  feet  wide 
through  the  roofs,  and  down  the  north  and  south  walls 
to  within  two  feet  of  the  ground.  In  the  west  room  is 
mounted,  on  sand-stone  piers,  a  transit  instrument,  made 
by  Ertel  and  Son,  of  Munich,  which  was  received  in 
1844.  The  object-glass  is  four  and  a  half  inches  clear 
aperture  and  76  inches  focal  length.  It  has  a  reversing 
stand,  by  which  the  Instrument  can  be  reversed  in  a 
minute  and  a  half.  This  instrument  cost  $1180,  be- 
sides the  expenses  of  transporting  it  from  Munich.  There 
is  also  in  this  room*  a  good  sidereal  clock  by  Molineux, 
of  London. 

In  the  east  room  is  mounted  on  two  massive  piers  a 
45  inch  meridian  circle,  made,  in  1845,  by  William 
Simms,  of  London,  with  a  telescope  five  feet  long,  and  a 
4  inch  object-glass.  The  circle  is  graduated  to  five 
minutes,  and  there  are  four  micrometers  fixed  to  the 
eastern  pier,  reading  to  one  second  of  arc.  When  the  in- 


240  HISTORY   OF  ASTRONOMY. 

strument  is  reversed,  the  readings  are  made  by  a  second 
set  of  microscopes,  which  are  attached  to  the  western  pier. 
In  the  eye-tube  are  seven  fixed  and  one  movable  vertical 
wire,  with  one  fixed  and  one  movable  horizontal  wire. 
The  lowest  eye-piece  is  used  for  a  collimating  eye-piece, 
by  Which  the  nadir  point  is  determined  by  reflection 
from  a  vessel  of  mercury.  The  cost  of  this  instrument 
was  $2050.  With  this  instrument  there  is  a  fine  sidereal 
clock  by  Molineux,  of  London. 

This  observatory  is  under  the  direction  of  Eev.  James 
Curley,  who  commenced  a  series  of  transit  observations 
in  1846.  During  the  autumn  of  the  same  year,  he  made 
some  observations  of  circumpolar  stars  with  the  meridian 
circle,  for  determining  the  latitude  of  the  observatory. 
During  the  year  1848,  M.  Sestini,  of  Eome,  was  added  to 
this  observatory,  and  it  was  expected  that  the  celebrated 
^cornet  hunter  M.  De  Yico,  of  Rome,  would  be  associated 
with  Mr.  Curley.  But  these  expectations  were  suddenly 
disappointed  by  the  death  of  M.  De  Yico,  which  took  place 
at  London,  in  November,  1848. 

In  1852,  Mr.  Curley  published  a  quarto  volume  of  216 
pages,  under  the  title  of  "Annals  of  the  Astronomical 
Observatory  of  Georgetown  College,"  giving  a  descrip- 
tion of  the  observatory,  as  well  as  the  transit  instrument 
and  meridian  circle,  and  intimating  that  additional  num- 
bers of  the  "  Annals"  might  be  expected  hereafter. 


ASTKONOMICAL  OBSERVATOKIES. 


241 


CINCINNATI  OBSEEYATOEY. 

The  Cincinnati  observatory  owes  its  existence  to  the 
labors  of  Professor  O.  MJMjfrdiftll.  Tn  il™  years  1841 
and  1842,  a  society  was  organized  in  Cincinnati,  called 
the  Cincinnati  Astronomical  Society,  the  object  of  which 
was  to  furnish  the  city  with  an  observatory.  Eleven 
thousand  dollars  were  subscribed  in  shares  of  twenty -five 
dollars  each ;  and  a  site  for  the  building  was  given  by 
Nicholas  Longworth,  Esq.  It  consists  of  four  acres  of 
ground  on  one  of  the  highest  hills  on  the  eastern  side  of 


CINCINNATI   OBSEBVATOEV. 


the  town.  In  June,  1842,  Professor  Mitchell  visited 
Europe  to  purchase  a  telescope.  At  Munich,  he  found 
an  object-glass  of  12  inches  aperture,  which  had  been 

tested  by  Dr.  Lamont,  and  pronounced  one  of  the  best 

11 


242 


HISTORY   OF  ASTRONOMY. 


ever  manufactured.  This  was  subsequently  ordered  to 
be  mounted,  and  was  purchased  for  $9437.  The  instru- 
ment arrived  in  Cincinnati  in  February,  1845.  In 
November,  1843,  the  corner-stone  of  the  observatory 


CINCINNATI  TELEBOOPB. 


was  laid  by  the  venerable  John  Quincy  Adams.  The 
building  is  80  feet  long  and  30  broad.  Its  front  presents 
a  basement  and  two  stories ;  while  in  the  center  the  build- 


ASTRONOMICAL  OBSERVATORIES .  24:3 

ing  rises  three  stories  in  height.  The  pier  is  built  of 
stone,  and  is  grouted  from  its  foundation  on  the  rock  to 
the  top.  The  equatorial  room  is  25  feet  square,  and  is 
surmounted  by  a  roof  so  arranged  that  it  may  be  entirely 
removed  during  the  time  of  observations. 

The  object-glass  of  the  telescope  has  an  aperture  of  12 
inches,  and  a  focal  length  of  17  feet.  The  hour  circle  is 
16  inches  in  diameter,  and  reads  by  two  verniers  to  two 
seconds.  The  declination  circle  is  26  inches  in  diameter, 
and  divided  on  silver  to  five  minutes,  reading  by  verniers 
to  four  seconds.  The  instrument  has  five  common  eye- 
pieces and  nine  micrometrical,  with  powers  varying  from 
100  to  1400.  It  is  furnished  with  clock-work,  by  which 
a  star  is  kept  steadily  in  the  field  of  view  of  the  tele- 
scope. 

Through  the  liberality  of  Dr.  Bache,  the  superintendent 
of  the  United  States  Coast  Survey,  this  observatory  has 
been  furnished  with  a  five  feet  transit  instrument ;  and  a 
new  sidereal  clock  has  recently  been  received. 

Professor  Mitchell  has  hitherto  devoted  much  of  his 
time  to  the  measurement  of  Struve's  double  stars  south 
of  the  equator.  A  number  of  interesting  discoveries  have 
been  made  in  the  course  of  this  review.  Stars  which 
Struve  marked  as  oblong,  have  been  divided  and  meas- 
ured ;  others  marked  doubk,  have  been  again  subdivided 
and  found  to  be  triple  ;  while  a  comparison  of  the  recent 
measures  of  distance  and  position  with  the  measurements 
of  Struve,  has  demonstrated  the  physical  connection  of 
the  components  of  many  of  these  stars. 


244  HISTOEY  OF  ASTRONOMY. 

For  the  last  two  or  three  years  the  energies  of  Professor 
Mitchell  have  been  devoted  almost  exclusively  to  railroad 
engineering,  and  the  observatory  has  consequently  been 
neglected.  We  trust  that  he  will  soon  free  himself  from 
such  groveling  occupations,  and  again  direct  the  gaze  of 
his  powerful  telescope  to  study  the  movements  of  distant 
worlds. 

CAMBRIDGE  OBSERVATORY. 


The  project  of  erecting  an  observatory  in  the  neighbor- 
hood of  Boston  upon  a  scale  corresponding  with  the  im- 
portance and  dignity  of  astronomy,  had  for  a  long  period 
been  the  subject  of  conversation  among  the  friends  of 
science.  This  was  a  favorite  scheme  with  John  Q.  Adams, 
Nathaniel  Bowditch,  and  others,  and  various  plans  had 
been  proposed  for  carrying  it  into  execution ;  but  it  did 
not  appear  practicable  to  raise  a  sum  of  money  sufficient 
to  complete  the  plan  upon  the  liberal  scale  which  was  de- 
sired. Something  was  needed  to  give  a  stronger  impulse 
Sto  the  claims  of  practical  astronomy.  This  impulse  was 
given  by  the  unexpected  appearance  of  the  splendid  comet. 

I 


ASTRONOMICAL   OBSERVATORIES.  245 

of  1843.  In  the  month  of  March  of  that  year,  a  comet 
with  a  long  and  brilliant  train  having  made  its  appear- 
ance, the  people  of  Boston  naturally  looked  to  the  as- 
tronomers of  Cambridge  for  information  respecting  its 
movements.  The  astronomers  replied  that  they  had  no 
instruments  adapted  to  nice  cometary  observations.  This 
announcement,  together  with  the  knowledge  ef  the  exist- 
ence of  good  instruments  in  other  parts  of  the  United 
States,  aroused  the  general  determination  to  supply  the 
deficiency.  Definite  action  was  taken  in  March,  1843. 

An  informal  meeting  of  a  few  individuals  interested 
in  the  subject  was  held  at  the  office  of  the  American 
Insurance  Company  in  Boston.  The  proceedings  of  this 
meeting  were  cordially  seconded  by  the  American 
Academy  of  Arts  and  Sciences,  and  a  full  meeting  of 
merchants  and  other  citizens  of  Boston  was  subsequently 
held  at  the  hall  of  the  Marine  Society,  to  consider  the 
expediency  of  procuring  a  telescope  of  the  first  class  for 
astronomical  observations.  At  this  meeting  the  question 
was  decided  in  the  affirmative,  and  a  subscription  of 
twenty  thousand  dollars  recommended  to  defray  the 
expense.  This  amount  was  soon  furnished.  Mr.  David 
Sears,  of  Boston,  gave  five  thousand  dollars  for  the  erec- 
tion of  an  observatory,  besides  five  hundred  dollars 
toward  the  telescope.  Another  gentleman  of  Boston 
gave  one  thousand  dollars  for  the  same  object;  eight 
other  gentlemen  of  Boston  and  its  vicinity  gave  five 
hundred  dollars  each;  there  were  eighteen  subscribers 
of  two  hundred  dollars  each ;  and  thirty  of  one  hundred 


246 


HISTORY  OP   ASTRONOMY. 


dollars  each,  besides  many  smaller  sums.  The  American 
Academy  of  Arts  and  Sciences  made  a  donation  of  three 
thousand  dollars;  the  Society  for  the  Diffusion  of  Use- 
ful Knowledge  gave  one  thousand  dollars ;  the  American, 


Merchants7,  and  National  Insurance  Companies  and 
Humane  Society  gave  five  hundred  dollars  'each ;  two 
other  companies  gave  three  hundred  dollars  each ;  one 


ASTRONOMICAL   OBSERVATORIES.  247 

gave  two  hundred  and  fifty,  and  another  gave  two  hun- 
dred dollars. 

The  Corporation  of  Harvard  University  purchased  an 
excellent  site  for  the  erection  of  an  observatory.  The 
ground  comprises  about  six  and  a  half  acres.  The  posi- 
tion is  elevated  about  50  feet  above  the  general  plain  on 
which  are  erected  the  buildings  of  the  University ;  and 
it  commands  in  every  direction  a  clear  horizon,  without 
obstruction  from  trees,  houses,  smoke,  or  other  causes. 
Upon  this  spot,  which  is  known  as  Summer  House  Hill, 
the  Sears  Tower  was  erected  for  the  accommodation  of 
the  large  telescope,  with  wings  for  other  instruments, 
and  a  house  for  the  observer.  The  Sears  Tower  is  a 
brick  building  32  feet  square,  resting  on  a  granite  found- 
ation. The  corners  of  the  towers  are  arched  so  as 
gradually  to  bring  the  interior  into  a  circular  form  of  31 
feet  diameter,  surmounted  by  a  granite  circle,  on  which 
is  laid  an  iron  rail  hollowed  in  the  middle  to  serve  as  a 
track  for  the  iron  balls  on  which  the  dome  revolves. 
The  dome  has  a  diameter  of  30  feet  on  the  inside,  with 
an  opening  five  feet  wide,  extending  beyond  the  zenith. 
The  shutters  to  this  opening  are  raised  and  closed  by 
means  of  endless  chains  working  in  toothed  wheels.  To 
the  lower  edge  of  the  dome  is  affixed  a  grooved  iron 
rail  similar  to  the  one  laid  on  the  granite  cap  of  the 
walls,  and  the  dome  rests  on  eight  iron  balls,  which  had 
been  smoothly  turned,  and  were  placed  at  equal  dis- 
tances round  the  circle.  Although  this  dome  is  es- 
timated to  weigh  about  fourteen  tons,  yet  it  can  be 


248  HISTORY   OF   ASTRONOMY. 

turned  through  a  whole  revolution  by  a  single  individual, 
without  any  very  great  exertion,  in  thirty -five,  seconds. 

The  central  pier  for  the  support  of  the  telescope  is 
of  granite,  and  is  in  the  form  of  ^  frustum  of  a  cone 
22  feet  in  diameter  at  the  base,  and  10  feet  at  the  top. 
It  is  40  feet  high,  and  rests  on  a  wide  foundation  of 
.grouting  composed  of  hydraulic  cement  and  coarse 
gravel,  26  feet  below  the  natural  surface  of  the  ground, 
and  is  entirely  detached  from  every  other  part  of  the 
building.  Upon  the  top  of  the  pier  is  laid  a  circular 
cap-stone,  10  feet  in  diameter,  and  2  feet  thick,  on  which 
stands,  by  three  bearings,  the  granite  block,  10  feet  in 
height,  to  which  the  metallic  bed-plate  of  the  telescope 
is  firmly  attached  by  bolts  and  screws.  Five  hundred 
tons  of  granite  were  used  in  the  construction  of  this 
pier. 

Upon  the  east  side  of  this  tower  is  a  small  wing  for 
the  accommodation  of  the  transit  circle  and  clock ;  and 
on  the  north  side  is  a  similar  wing,  designed  for  a  transit 
in  the  prime  vertical.  The  house  for  the  accommodation 
of  the  observer  is  connected  with  the  east  wing.  The 
western  wing  is  used  for  magnetic  and  meteorological 
observations.  This  wing  was  erected  in  the  years 
1850-51,  making  the  entire  length  of  the  building  160 
feet,  and  adds  greatly  to  the  architectural  beauty  of  the 
observatory.  In  the  small  dome  is  placed  the  smaller 
equatorial,  of  5  feet  focal  length,  and  4  and  1-8  inch 
aperture,  made  by  Merz,  which  is  a  remarkably  fine 
instrument. 


ASTRONOMICAL  OBSERVATORIES.  249 

The  "  Grand  Kefractor"  was  made  by  Messrs.  Merz 
and  Mahler,  of  Munich,  Bavaria.  .  They  bound  them- 
selves by  contract  to  make  two  object-glasses  of  the  clear 
aperture  of  15  inches,  to  be  at  least  equal  to  that  fur- 
nished for  the  noble  instrument  now  mounted  at  the 
Eussian  observatory  at  Pulkova.  Oil  being  notified  of 
the  completion  of  these  object-glasses,  the  agent  of  the 
University,  Mr.  Cranch,  of  London,  accompanied  by  the 
instrument-maker,  Mr.  Simms,  proceeded  to  Munich,  and 
after  careful  trial  and  examination,  made  the  required 
selection.  The  selected  object-glass  was  received  at 
Cambridge  in  December,  1846;  the  great  tube  and  its 
equatorial  mounting  did  not  arrive  until  June,  1847.  The 
object-glass  of  the  telescope  is  15  inches  in  diameter, 
and  has  22  feet  6  inches  focal  length.  Some  of  the 
eye-pieces  are  6  inches  long,  making  the  entire  length  23 
feet.  The  telescope  has  eighteen  different  powers,  rang- 
ing from  103  to  2000.  The  hour  circle  is  18  inches  in 
diameter,  divided  on  silver,  and  reading  by  two  verniers 
to  one  second  of  time.  The  declination  circle  is  26 
inches  in  diameter,  divided  on  silver,  and  reads  by  four 
verniers  to  four  seconds  of  arc.  The  movable  portion 
of  the  telescope  and  machinery  is  estimated  to  weigh 
about  three  tons.  It  is,  however,  so  well  counterpoised 
in  every  position  of  the  telescope,  and  the  effects  of 
friction  are  so  far  obviated  by  an  ingenious  arrangement 
of  rollers  and  balance-weights,  that  the  observer  can 
direct  the  instrument  to  any  part  of  the  heavens  by  a 
slight  pressure  of  the  hand  upon  the  ends  of  the  balance 

11* 


250 


HISTORY   OF  ASTRONOMY. 


rods.  A  sidereal  motion  is  given  to  the  telescope  by 
clock-work,  regulated  by  centrifugal  balls,  by  -which 
means  a  celestial  object  may  be  kept  constantly  in 
the  field  of  view.  The  cost  of  this  instrument  was 
$19,842. 


CAMBRIDGE  EQTTATOBIAL. 


The  optical  character  of  this  instrument  has  given 
entire  satisfaction.  The  components  of  the  star  Gamma 
Ooronse,  which  Struve,  with  the  Pulkova  refractor,  pro- 


ASTRONOMICAL  OBSERVATORIES.  251 

nounces  most  difficult  to  separate,  being  distant  from  each 
other  less  than  half  a  second,  are  seen  in  the  Cambridge 
telescope  distinct  and  round,  and  the  dark  space  between 
jfined.     The  components  of  Gamma 
\  are  distant  from  each  other  less  than 
ilso  separated  with  equal  distinctness. 
Antares,  estimated  to  be  of  the  tenth 
ich  was  discovered  by  Professor  Mit- 
ncinnati    refractor,   is   quite   conspic- 
of  700.     It  was  with  this  instrument 
3d  the  eighth  satellite  of  Saturn,  two 
liscovered  by  Mr.  Lassell,  of  Liverpool, 
,n  reflector  of  21  inches  aperture.     He 
sfactory  micrometric  measurements  of 
jptune,  which  is  not  known  to  have 
ly  other  instruments  except  Mr.  Las- 
the  Pulkova  refractor.     The  minutest 
neighborhood  of  the  ring  nebula  of 
JT  Lord  Kosse  as  difficult  objects  with 
*,  are  seen  in  the  Cambridge  telescope. 


252  HISTORY   OF  ASTRONOMY. 

Mahler,  has  an  aperture  of  four  and  one  eighth  inches, 
and  a  focal  length  of  65  inches.  It  has  two  different 
modes  of  illumination;  one  through  the  axis  as  usual,- 
and  the  other  at  the  eye-piece,  showing  bright  wires  on 
a  dark  field.  Attached  to  the  eye-piece  are  two  microm- 
eters for  measures  both  in  altitude  and  in  azimuth. 

There  is  also  belonging  to  the  observatory  a  fine  comet- 
seeker,  by  Merz  and  Mahler,  having  an  aperture  of  four 
and  a  quarter  inches.  The  wing  on  the  north  side  of 
the  tower  is  designed  hereafter  to  receive  a  transit  in 
the  prime  vertical ;  but  this  instrument  has  not  yet  been 
ordered. 

During  the  summer  of  1848,  Mr.  Bond  being  engaged 
with  the  United  States  Coast  Survey  in  determining 
differences  of  longitude,  turned  his  attention  to  the  electro- 
magnetic method  of  recording  astronomical  observations. 
The  apparatus  adopted  at  this  observatory  consists  of  a 
Grove's  battery,  a  circuit-breaking  sidereal  clock,  and  a 
"  spring  governor."  These  are  connected  by  means  of 
copper  wires  leading  to  all  the  principal  instruments. 

The  spring  governor  is  a  machine  devised  to  carry  a 
cylinder  with  an  equable  rotary  motion,  so  that  it  may 
make  one  entire  revolution  in  one  minute  of  sidereal 
time.  A  sheet  of  paper  is  wrapped  round  the  cylinder, 
and  on  this  paper  the  commencement  of  each  second  is 
recorded  in  exact  coincidence  with  the  beats  of  the  clock. 
The  observer  at  each  telescope  is  furnished  with  a  break- 
circuit  key,  by  which  means  he  is  enabled  to  make  a 
record  of  his  observations  on  the  paper  covering  the 


ASTRONOMICAL  OBSERVATORIES.  253 

cylinder,  among  the  second  marks  of  the  clock,  in  such  a 
manner  that  the  tenths  of  a  second  may  be  read  off  with- 
out difficulty. 

The  clock  signals  are  also  readily  connected  with  the 
lines  of  the  telegraph  offices,  so  that  in  effect  the  beats  of 
the  Cambridge  clock  are  as  distinctly  heard  at  the  offices 
in  Boston,  Lowell,  and  elsewhere,  as  they  are  within  a  few 
feet  of  the  clock.  The  time  is  thus  given  all  along  the 
telegraph  lines,  and  this  is  found  highly  useful  in  regula- 
ting the  starting  of  the  railroad  trains. 

Mr.  "William  C.  Bond,  and  his  son,  George  P.  Bond, 
give  their  undivided  attention  to  the  objects  of  the  ob- 
servatory. For  the  first  four  or  five  years  after  receiving 
their  grand  refractor  they  gave  their  whole  strength  to 
that  class  of  observations  for  which  this  instrument  af- 
fords peculiar  advantages,  such  as  the  following:  ob- 
servations of  new  planets  ;  the  satellites  of  Saturn,  Ura- 
nus, and  Neptune ;  double  stars,  especially  such  as  have 
considerable  proper  motion  ;  together  with  a  general  re- 
view of  the  most  remarkable  nebulae.  They  have  pub- 
lished in  the  Memoirs  of  the  American  Academy,  a  de- 
scription of  the  great  nebula  in  Orion,  and  that  of  Andro- 
meda, accompanied  with  drawings  of  the  most  careful  and 
elaborate  execution. 

The  younger  Bond  for  several  years  maintained  a  con- 
stant and  systematic  search  for  comets.  With  the  comet- 
seeker  he  swept  over  the  entire  heavens  at  least  once  a 
month,  and  whenever  he  found  any  nebulous  body  with 
which  he  was  not  familiar,  it  was  subjected  to  a  special 


254  HISTORY   OF  ASTRONOMY. 

examination.  He  has  thus  been  the  independent  discov- 
erer of  eleven  comets,  but  unfortunately  it  subsequently 
appeared  that  each  of  .these,  save  one,  had  been  pre- 
viously discovered  in  Europe.  The  comet  of  August  29, 
1850,  he  discovered  seven  days  in  advance  of  the 
European  astronomers.  Two  other  comets  he  discovered 
on  the  same  night  that  they  were  seen  in  Europe,  viz., 
those  of  June  5,  1845,  and  April  11,  1849.  Having 
found  this  species  of  observation  too  severe  a  trial  for  his 
eyes,  he  has  for  the  last  three  or  four  years  given,  up 
comet-seeking  altogether. 

In  April,  1852,  the  Messrs.  Bond  commenced  a  series 
of  observations  which  contemplate  the  formation  of  a  most 
extensive  catalogue  of  stars  down  to  the  eleventh  magni- 
tude. For  this  purpose  they  inserted  in  the  focus  of  the 
great  equatorial  a  thin  plate  of  mica,  upon  which  were 
ruled  a  large  number  of  parallel  and  equidistant  lines, 
designed  to  measure  differences  of  declination ;  and  per- 
pendicular to  these  they  introduced  three  other  parallel 
lines  designed  for  observations  of  right  ascension.  The 
telescope  being  fixed  in  the  meridian,  with  the  first  set  of 
lines  parallel  to  the  horizon,  if  the  times  of  passage  of  any 
number  of  stars  over  the  vertical  lines  be  observed,  we 
shall  have  their  differences  of  right  ascension  ;  and  by  ob- 
serving near  which  of  the  horizontal  lines  they  traverse 
the  field  of  the  telescope,  we  shall  obtain  their  differences 
of  declination.  The  observations  of  right  ascension  are 
all  recorded  by  the  electro-magnetic  apparatus  in  the 
manner  already  described.  The  method  pursued,  there- 


ASTRONOMICAL  OBSERVATORIES.  255 

fore,  by  the  observer,  is  first  to  fix  the  telescope  firmly  at 
any  required  altitude,  and  then  applying  his  eye  to  thes 
telescope,  he  observes  each  star  in  succession  as  it  enters 
the  field  of  view.  One  night's  work  embraces  a  zone  ten 
minutes  in  breadth,  and  having  a  length  corresponding  to 
the  number  of  hours  for  which  the  observations  are  con- 
tinued. 

The  Messrs.  Bond  design  to  include  in  their  series  all 
stars  to  the  eleventh  magnitude,  and  as  many  of  the  twelfth 
as  can  be  got  without  interfering  with  the  determination 
of  the  brighter  ones.  Each  zone  is  observed  a  second 
time  as  soon  as  possible,  in  order  not  to  miss  any  chance 
of  finding  a  planet  which  might  happen  to  be  in  the  way ; 
but  as  the  object  is  not  planet-hunting,  this  is  not  allowed 
to  interfere  with  the  work,  further  than  that  missing  stars 
are  noted  and  looked  after.  It  seldom  happens  that 
the  disappearance  does  not  prove  to  have  originated  in 
some  mistake.  At  the  re-observations,  all  the  particulars 
of  the  first  observation  undergo  a  revision,  the  original 
notes  being  read  and  compared  as  the  star  passes  the 
field.  All  the  double  stars,  nebulae,  remarkable  groups, 
vacancies,  etc.,  are  recorded.  The  comparison  of  the 
places  of  stars  which  have  been  previously  observed  at 
other  observatories  forms  part  of  the  reduction ;  and  in 
this  way  they  have  detected  some  cases  of  considerable 
proper  motion. 

The  Messrs.  Bond  have  completed  two  entire  zones 
(each  twice  observed)  for  the  whole  circuit  of  the  heavens, 
from  the  equator  to  '20  minutes  of  north  declination. 


256  HISTORY  OF  ASTRONOMY. 

These  have  been  completely  reduced,  and  were  published 
in  1855,  under  the  title  of  "  Annals  of  the  Astronomical 
Observatory  of  Harvard  College,  vol.  I.,  part  2."  These 
two  zones  contain  5500  stars.  The  Messrs.  Bond  are 
now  carrying  on  simultaneously,  and  have  nearly 
completed,  two  zones  from  20  to  40  minutes  north  de- 
clination. 

The  resources  of  this  observatory  have  recently  been 
very  much  increased  by  the  munificence  of  Edward  B. 
Phillips,  a  graduate  of  the  University  in  the  class  of  1845. 
Mr.  Phillips  died  in  1848,  and  bequeathed  to  the  observa- 
tory $100,000  as  a  perpetual  fund,  the  interest  to  be  ap- 
plied annually  to  the  payment  of  the  salaries  of  the  ob- 
servers, or  for  instruments,  or  a  library  for  the  use  of  the 
observatory,  at  the  discretion  of  the  corporation  of  the 
college,  who  are  made  the  trustees  of  the  fund.  This  sum 
was  paid  to  the  college  by  Mr.  Phillips's  executors  in 
September,  1849. 

SHARON  OBSERVATORY. 

Sharon  observatory  is  a  private  establishment  belong- 
ing to  the  late  Mr.  John  Jackson,  situated  near  Darby, 
about  seven  miles  west  of  Philadelphia.  It  was  erected 
in  1845,  is  17  feet  square  on  the  outside,  and  rises  to  the 
height  of  34  feet.  At  five  feet  from  the  top,  two  strong 
beams  are  placed  across  the  building,  and  support  a  cir- 
cular platform  of  five  feet  diameter,  on  which  the  equa- 
torial stands.  The  tower  is  surmounted  by  a  conical 
dome,  which  rests  on  four  iron  balls  revolving  in  a  circu- 


ASTRONOMICAL   OBSERVATORIES. 


257 


lar  railway.  The  opening  in  the  dome  is  18  inches  wide, 
and  has  three  doors  which  slide  over  each  other,  and  are 
moved  by  cords  passing  over  pulleys. 


8HABOX  OBSBEVATOET. 


The  equatorial  was  made  by  Merz  and  Son,  of  Munich? 

It  was  ordered  in  1842,  and  arrived  in  1846.  The  ob- 
ject-glass has  a  clear  aperture  of  six  and  a  third  inches, 
and  its  focal  length  is  nearly  nine  feet.  It  has  a  microm- 
eter with  a  large  number  of  eye-pieces  magnifying  from 
85  to  456  times.  The  hour  circle  is  9  inches  in  diameter, 
and  the  declination  circle  is  13  inches.  Clock-work  is 
attached  to  the  polar  axis,  giving  to  the  telescope  a  uni- 
form motion,  and  keeping  a  star  apparently  at  rest  in  the 
field  of  view.  The  entire  expense  of  this  instrument  was 
$1833. 

This  observatory  is  also  furnished  with  a  meridian 


258  HISTORY  OF   ASTRONOMY. 

circle  made  by  Young,  of  Philadelphia  ;  the  object  glass 
having  been  procured  from  Merz  and  Son,  of  Munich. 
It  is  mounted  on  a  marble  column,  resting  on  solid 
masonry,  in  the  south  wall  of  the  tower.  The  object- 
glass  is  three  and  a  quarter  inches  in  diameter,  and  has  a 
focal  length  of  four  feet.  One  end  of  the  axis  carries  a 
circle  20  niches  in  diameter,  which  is  graduated  to  four 
minutes,  and  reads  by  four  verniers  to  three  seconds. 
The  price  of  this  instrument  was  $800.  A  sidereal  clock 
is  supported  by  a  marble  column  near  the  meridian  circle. 
It  has  a  mercurial  pendulum,  and  was  made  by  Gropen- 
giesser,  of  Philadelphia.  The  entire  cost  of  this  observa- 
tory, with  the  instruments,  was  $4000.  The  equatorial  is 
employed  in  the  observation  of  eclipses,  occupations,  and 
other  celestial  phenomena. 

TUSCALOOSA  OBSERVATORY,  ALABAMA. 

>  The  Tuscaloosa  observatory  was  erected  in  the  year 
1843,  and  has  been  furnished  with  instruments  for  ob- 
servation of  a  superior  order.  It  is  situated  upon  an 
elevation  distant  a  few  hundred  yards  from  the  Univer- 
sity buildings,  in  a  south-west  direction.  It  is  built  of 
brick,  and  is  55  feet  in  length  by  22  in  breadth  in  the 
center.  The  central  apartment  is  22  feet  square,  and  is 
surmounted  by  a  revolving  dome  of  18  feet  internal 
diameter,  under  which  is  mounted  the  equatorial  tele- 
scope made  by  Simms,  of  London.  This  instrument  was 
received  in  the  spring  of  1849.  Its  object-glass  has  a 
clear  aperture  of  eight  inches,  and  a  focal  length  of  12 


ASTRONOMICAL  OBSERVATORIES. 


259 


feet.  It  rests  upon  a  pier  of  masonry  which  rises  11  feet 
above  the  floor  of  the  room.  The  hour  circle  has  a 
diameter  of  18  inches,  with  verniers  which  read  to  one 
second  of  time.  The  declination  circle  has  a  diameter  of 
30  inches,  with  verniers  which  read  to  five  seconds  of 
arc.  This  instrument  is  moved  by  clock-work,  and  has  a 
variety  of  magnifying  powers  from  44  to  1640 ;  also  a 
filar  micrometer,  and  a  double-image  micrometer.  A 
movable  platform  runs  around  the  room  at  the  height  of 
eight  feet  from  the  floor,  and  gives  easy  access  to  the 
object-end  of  the  telescope  and  the  graduated  circles. 
This  telescope  cost  £800  sterling.  In  the  same  room  is  a 
clock  with  mercurial  compensation  by  Molineux,  of  Lon- 
don, which  is  attached  to  a  solid  pier  unconnected  with 
the  floor  or  walls. 


TCSCAJ.OOSA  OBSERVATORY. 


The  west  wing  is  16  feet  square,  and  is  occupied  by  a 
transit  circle  made  in  1840  by  Simms,  of  London.  Its 
telescope  has  a  focal  length  of  five  feet,  and  an  object- 


260  HISTORY   OF  ASTRONOMY. 

glass  of  four  inches  clear  aperture.  Its  axis  carries  a 
circle  of  three  feet  diameter,  connected  with  it  by  twelve 
stout  conical  radii.  The  circle  is  graduated  upon  silver 
to  five  minutes,  and  reads  by  four  microscopes  to  single 
seconds.  The  whole  instrument  is  mounted  upon  massive 
cast-iron  pillars,  which  rest  upon  masonry,  and  rise  five 
feet  above  the  floor.  An  opening  18  inches  wide  is  cut 
through  the  roof,  and  extends  down  the  north  and 
south  walls  to  within  30  inches  of  the  floor.  In  the 
same  room  is  an  excellent  sidereal  clock  by  Dent,  of 
London. 

The  east  wing  is  fitted  up  for  an  office,  with  fire-place, 
cases  for  books,  etc. 

Beside  the  fixed  instruments  here  mentioned,  the  ob- 
servatory possesses  a  portable  transit  instrument,  an 
achromatic  refractor  of  7  feet  focal  length,  a  reflecting 
circle  of  10  inches  diameter,  standard  barometer,  etc. 

The  University  has  a  separate  building  for  a  magnetic 
observatory,  and  possesses  a  declination  instrument  and 
a  dipping  needle,  both  made  by  Gambey,  of  Paris. 

MR.  RUTHERFORD'S  OBSERVATORY. 

There  is  a  private  observatory,  erected  in  the  upper 
part  of  the  city  of  New  York,  corner  of  Second  Avenue 
and  Eleventh-street,  belonging  to  Lew,is  M.  Eutherford, 
Esq.  It  is  furnished  with  a  refracting  telescope,  made  by 
Henry  Fitz,  of  New  York.  The  aperture  of  the  object- 
glass  is  nine  inches,  and  its  focal  length  nine  and  a  half 
feet.  It  was  mounted  equatorially,  with  clock-work,  like 


ASTRONOMICAL  OBSERVATORIES.  261 

the  Dorpat  telescope,  by  Messrs.  Gregg  and  Rupp,  of 
New  York.  The  hour  circle  is  eighteen  inches  in 
diameter,  and  the  declination  circle  eleven  inches.  The 
telescope  has  four  eye-pieces,  the  highest  magnifying  600 
times.  The  price  of  this  instrument,  including  clock- 
work and  micrometer,  was  $2,200.  The  telescope  rests 
upon  a  brick  column,  surmounted  by  a  revolving  dome 
of  twelve  feet  diameter. 

Connected  with  this  observatory  is  a  small  building- 
containing  a  transit  instrument  by  Simms,  belonging  to 
Columbia  College.  The  telescope  has  an  aperture  of 
nearly  three  inches,  and  a  focal  length  of  four  feet.  It  is 
mounted  upon  two  stone  columns,  resting  upon  a  solid 
foundation  of  sandstone.  An  opening  in  the  roof  affords 
a  view  of  about  160  degrees  of  the  meridian.  In  a  small 
wing  of  this  building  is  a  stone  column,  upon  which  is 
placed  an  altitude  and  azimuth  instrument  by  Simms, 
also  belonging  to  Columbia  College.  The  horizontal  and 
vertical  circles  are  each  fifteen  inches  in  diameter, 
graduated  to  five  minutes,  and  reading  by  two  micro- 
scopes to  one  second  of  arc.  The  telescope  has  an  aper- 
ture of  two  inches,  and  a  focal  length  of  twenty-four 
inches. 

During  the  summer  of  1848,  this  observatory  was 
employed  by  the  Coast  Survey  as  a  station  for  determin- 
ing the  difference  of  longitude  between  Cambridge  and 
New  York  by  means  of  the  electric  telegraph. 


262  HISTORY  OF  ASTRONOMY. 

FRIENDS'  OBSERVATORY,   PHILADELPHIA. 

This  observatory  is  situated  in  the  city  of  Philadelphia, 
about  400  feet  east  of  Independence  Hall.  It  was  built 
in  1846,  and  has  a  revolving  dome  fifteen  feet  in 
diameter.  In  the  center  is  the  stand  for  the  equatorial, 
which  rests  on  the  walls  of  the  building,  unconnected 
with  the  floor  of  the  observatory.  The  principal  instru- 
ment is  a  refracting  telescope  of  five  inches  aperture,  and 
seven  feet  focal  length,  made  by  Henry  Fitz,  of  New 
York,  and  mounted  equatorially  after  the  manner  of 
Fraunhofer,  by  William  J.  Young,  of  Philadelphia.  The 
hour  circle  is  nine  inches  in  diameter,  and  the  declination 
circle  twelve  inches. 

A  twenty -inch  transit  instrument  is  permanently  placed 
on  a  pier  built  on  the  wall  of  the  building.  A  clock, 
with  a  mercurial  pendulum,  made  by  J.  L.  Gropengiesser, 
of  Philadelphia,  is  placed  on  a  pier  adjoining  the  transit 
instrument.  The  observatory  has  also  a  portable  refract- 
ing telescope  of  three  inches  aperture,  and  forty-two 
inches  focal  length,  made  by  Chevalier,  of  Paris,  and  a 
comet-seeker  of  three  inches  aperture,  mounted  on  a 
tripod,  made  by  Henry  Fitz,  of  New  York. 

Since  the  establishment  of  this  observatory,  occulta- 
tions,  eclipses,  etc.,  have  been  regularly  observed  by  the 
director,  Mr.  Miers  Fisher  Longstreth,  who  has  recently 
distinguished  himself  by  his  successful  labors  in  the 
construction  of  new  Luiiar  Tables. 


ASTRCXtfDMICAL  OBSERVATORIES. 


263 


AMHERST  COLLEGE  OBSERVATORY. 


A  small  building  for  astronomical  observations  was 
erected  in  1847  in  connection  with  Amherst  College, 
Massachusetts.  This  building  consists  of  an  octagonal 
tower  fifty  feet  high,  and  seventeen  feet  in  diameter,  with 
a  revolving  dome,  and  a  central  pedestal  for  supporting 
a  telescope.  On  the  east  side  of  the  tower  is  attached  a 
transit  room,  13  by  15  feet,  with  a  sliding  roof.  Here 
is  mounted  a  transit  circle,  made  by  Grambey,  of  Paris, 
the  telescope  having  a  focal  length  of  about  three  feet, 
and  an  aperture  of  two  and  a  half  inches.  The  circle 
is  fifteen  inches  in  diameter,  graduated  to  five  minutes, 
and  is  furnished  with  four  verniers  reading  to  three 
seconds.  The  clock  was  made  by  Breguet,  and  has  a 
gridiron  pendulum. 


! 


264  HISTORY   OF  ASTRONOMY. 

A  large  telescope,  manufactured  by  Mr.  Alvan  Clark, 
of  Cambridge,  Massachusetts,  has  recently  been  received, 
and  mounted  under  the  dome.  The  aperture  of  this 
telescope  is  seven  and  a  quarter  inches,  and  its  focal 
length  eight  and  a  half  feet.  A  block  of  stone,  weighing 
about  1800  pounds,  standing  on  the  top  of  the  brick 
pier,  supports  the  instrument.  The  top  of  the  stone  is 
level,  and  a  frame  of  cast-iron,  clamped  to  the  stone, 
sustains  the  polar  axis.  The  clock,  which  gives  the 
equatorial  movement,  is  let  into  the  top  of  the  stone, 
and  is  regulated  by  a  pendulum,  while  the  motion  is 
rendered  continuous  and  nearly  uniform  by  means  of  an 
elegant  contrivance  of  Professor  W.  C.  Bond,  called  the 
spring  governor.  With  this  telescope  Mr.  Clark  dis- 
covered two  new  double  stars,  in  one  of  which  the  dis- 
tance of  the  components  is  but  three-tenths  of  a  second. 
This  instrument  cost  $1,800,  and  was  presented  to  Am- 
herst  College  by  Hon.  Rufus  Bulloch,  of  Eoyalston. 

CHARLESTON  OBSERVATORY,  SOUTH  CAROLINA. 

This  observatory  was  built  by  Professor  Lewis  K. 
in  his  own  garden  in  Charleston.  It  is  a  wooden 
building  of  10  by  15  feet,  with  a  sliding  roof.  It  con- 
tains a  five  feet  transit  instrument,  by  Troughton,  solidly 
mounted  on  a  pier  of  red  sandstone,  and  commands  the 
meridian  to  within  ten  degrees  of  the  horizon  on  either 
side.  There  is  also  a  five  feet  telescope,  by  Adams,  of 
London,  mounted  equatorially,  and  provided  with  a  po- 
sition micrometer,  by  Troughton  and  Simms,  and  two 


ASTRONOMICAL   OBSERVATORIES. 

chronometers,  by  Hutton,  of  London,  one  sidereal  and 
the  other  solar.  The  instruments  all  belong  to  the  Coast 
Survey,  except  the  equatorial  telescope. 

Observations  were  commenced  by  Professor  Gibbes  in 
April,  1848,  on  moon  culminations  and  occupations  for 
the  use  of  the  Coast  Survey  ^  and  have  been  continued 
to  the  present  time.  In  February,  1850,  this  observatory 
was  connected  by  the  telegraph  wires  with  the  obser- 
vatory at  Seaton  Station,  "Washington  City,  for  difference 
of  longitude  by  the  electro-chronographic  method.  In 
March,  1851,  it  was  connected  in  a  similar  manner  with 
a  temporary  observatory  in  Savannah,  Georgia,  and  a 
successful  series  of  observations  made  for  the  difference 
of  longitude  of  the  two  stations.  During  the  winter  and 
spring  of  1852,  another  telegraph  comparison  for  longi- 
tude was  made  between  Charleston  and  Washington, 
which  proved  entirely  successful. 

DARTMOUTH   COLLEGE   OBSERVATORY. 

The  founding  of  Dartmouth  College  observatory  was 
due  chiefly  to  the  munificence  of  the  late  George  C. 
Shattuck,  M.D.,  LL.D.,  of  Boston,  who  furnished  the 
means  for  the  erection  of  the  building,  the  purchase  of 
the  meridian  circle,  the  comet-seeker,  a  chronometer,  etc., 
together  with  a  large  part  of  the  books  belonging  to  the 
library.  The  site  of  the  building  is  near  the  summit  of 
an  isolated  hill,  about  50  rods  north-east  of  the  college 
green,  and  .elevated  70  feet  above  it,  commanding  a 
charming  prospect  up  and  down  the  Valley  of  the  Connec- 

12 


266 


HISTORY  OP  ASTRONOMY.. 


ticut.  The  principal  south  meridian  mark  is  situated  on 
the  bare  summit  of  a  hill  two  miles  distant,  at  an  eleva- 
tion of  less  than  two  degrees  above  the  level  of  the  transit 
circle. 


i** 


'.UITMOUTII  COLI.i:.:K   OB8EBVATOBY. 


The  observatory  is  of  brick,  with  double  walls  fifteen 
inches  thick,  inclosing  a  six-inch  space  of  air  between 
them  ;  and,  as  the  cornice  and  the  partitions  are  also  of 
brick,  and  the  roof  covered  with  tin,  it  is  nearly  fire- 
proof. The  building  consists  of  a  central  two-story  ro- 
tunda, 20  feet  in  diameter,  with  three  one-story  wings — 
one  on  the  east,  measuring  35  by  16  feet,  and  the  other 
two  on  the  north  and  south,  each  20  by  16  feet.  The 
foundations  of  the  walls  and  of  the  piers  all  rest  upon 
the  solid  rock — sienitic  gneiss — at  depths  varying  from 
zero  to  14  feet  below  the  underpinning.  The  lower  cir 


ASTRONOMICAL  OBSERVATORIES.  267 

cular  room  in  the  rotunda,  17  feet  in  diameter,  is  in- 
tended for  a  library,  and  communicates  directly  with  the 
observer's  rooms  in  the  north  and  south  wings.  The 
square  brick  equatorial  pier,  four  feet  in  diameter,  rises 
through  the  middle  of  the  room  without  touching  the 
flooring  or  ceiling,  and  is  capped  with  a  cylindrical 
granite  block  nearly  6  feet  in  diameter,  and  15  inches 
thick.  The  pier  contains  a  Tecess,  having  double  glazed 
doors,  and  a  space  of  dead  air  on  all  sides,  for  the  recep- 
tion of  a  clock,  to  be  connected  with  an  electro-chrono- 
graph. The  pier  is  also  surrounded  by  the  book-shelves, 
which  are  entirely  detached  from  it. 

The  observer's  rooms  are  in  the  north  and  south  wings, 
and  are  each  21  by  14  feet,  and  have  each  a  slit  in  the 
roof  two  feet  wide,  the  north  one  having  a  corresponding 
pier  for  prime  vertical  observations. 

The  transit  room,  18  by  14  feet,  in  the  east  wing,  has 
two  slits,  the  eastern  one  having  a  corresponding  pair 
of  piers  for  the  meridian  circle,  and  the  other  a  single 
pier  for  the  use  of  portable  instruments.  The  entrance 
hall,  14  by  11  feet,  in  the  center  of  the  building,  opens 
directly  into  all  the  rooms  except  the  library. 

The  foundation  for  the  dome  of  the  equatorial  room 
consists  of  circular  segments  of  planks,  firmly  secured 
together,  and  bolted  to  the  walls  below.  Upon  this, 
and  directly  over  the  middle  of  the  inner  wall,  are 
screwed  twelve  segments  of  a  circular  cast-iron  rail, 
three  inches  wide,  with  a  circular  channel  three  eighths 
of  an  inch  deep.  Between  this  and  a  corresponding 


HISTORY  OF  ASTRONOMY. 

rail  attached  to  the  base  ring  of  the  dome,  are  placed  the 
six  cannon-balls,  each  six  inches  in  diameter,  on  which 
the  dome  revolves.  The  dome  itself  is  a  complete  hemi- 
sphere, 18  feet  in  diameter.  The  opening  for  the  tele- 
scope is  two  and  a  half  feet  wide,  and  extends  one  foot 
beyond  the  apex  of  the  dome.  The  opening  for  the 


GEOUND  PLAN  OF  DABXMOTJTH  COLLEGE  OB8EEVATOET. 

telescope  is  closed  by  three  shutters;  the  upper  one, 
about  10  feet  long,  moving  on  casters  over  an  iron  rail- 
way on  the  outside  of  the  dome.  The  two  lower  ones, 
about  two  and  a  half  feet  each,  rise  and  fall  by  means 
of  weights  in  the  manner  of  common  window-sashes. 
The  entire  dome  is  estimated  to  weigh  about  2800 


ASTRONOMICAL  OBSERVATORIES.  269 

pounds,  and  the  average  force  necessary  to  preserve  a 
uniform  velocity  of  rotation  is  found,  by  experimenting 
with  spring  steelyards,  to  be  about  six  pounds. 

The  equatorial  telescope  was  made  by  Merz  and  Sons, 
of  Munich;  and  has  a  clear  aperture  of  six  inches,  with 
a  focal  length  of  eight  and  a  half  feet.  It  has  seven 
negative  eye-pieces,  magnifying  from  36  to  600  times ; 
a  single  lens  magnifying  940  times  ;  a  prismatic  reflector, 
to  which  these  pieces  are  all  adapted ;  and  a  terrestrial 
eye -piece,  magnifying  80  times.  It  has  two  micrometers, 
one  a  ring  micrometer,  the  other  a  filar  position  microm- 
eter, having  11  equidistant  fixed  lines  perpendicular  to 
the  two  movable  ones,  and  may  be  illuminated  in  either 
a  dark  or  bright  field  at  pleasure.  It  has  five  positive 
eye-pieces,  magnifying  from  128  to  480  times.  The  hour 
circle  is  nine  and  a  half  inches  in  diameter,  and  the 
declination  circle  is  thirteen  inches  in  diameter.  The 
telescope  is  moved  in  right  ascension  by  an  adjustable 
centrifugal  clock. 

The  meridian  circle,  by  Simms,  of  London,  is  30  inches 
in  diameter,  divided  on  silver  to  spaces  of  five  minutes, 
with  two  reading  microscopes  fixed  to  the  piers,  and  a 
third  placed  at  a  small  distance  from  one  of  the  others, 
for  examining  and  determining  the  errors  of  graduation. 
The  telescope  has  a  clear  aperture  of  four  inches,  and  a 
focal  length  of  five  feet.  It  has  four  positive  eye-pieces, 
besides  one  for  collimating  by  means  of  a  mercurial 
trough.  It  is  furnished  with  a  declination  micrometer 
and  seven  equidistant  meridian  lines.  The  wires  can  be 


270  HISTORY   OF  ASTRONOMY. 

illuminated  in  a  dark  field,  or  the  reverse,  at  the  option 
of  the  observer.  The  granite  piers  for  this  instrument 
are  of  the  T  form,  gradually  diminishing  upward  to 
within  10  inches  of  the  top.  They  are  30  inches  apart, 
and  rise  5  feet  above  the  floor.  They  rest  on  a  granite 
foundation,  which  is  based  on  the  solid  rock  below. 

The  comet-seeker,  by  Merz  and  Sons,  has  an  aperture 
of  about  4  inches,  and  a  focal  length  of  32  inches.  It  is 
mounted  on  an  equatorial  stand,  and  has  4  eye-pieces, 
magnifying  from  12  to  40  times. 

The  sidereal  clock  is  furnished  with  Mahler's  compen- 
sation pendulum,  and  runs  a  month  without  winding. 
The  library  contains  about  500  volumes  of  the  most 
valuable  books  pertaining  to  theoretical  and  practical 
astronomy. 

The  cost  of  the  building,  exclusive  of  the  lot  and 
its  embellishments,  was  about  $4,500.  The  cost  of  the 
equatorial  telescope,  together  with  the  sidereal  clock, 
was  about  $2,300.  The.  comet-seeker  '  cost  $180 ;  and 
the  meridian  circle  cost  .£275  in  London. 

MR.  VAN  ARSDALE'S  OBSERVATORY,  NEWARK,  NEW  JERSEY. 

This  observatory  was  built  in  the  spring  of  1850.  It 
is  a  circular  wooden  building  13  feet  in  diameter,  resting 
on  a  brick  foundation,  underlaid  with  stone  to  the 
depth  of  two  feet.  The  circular  brick  foundation  is 
covered  with  wood-work  three  inches  in  thickness,  and 
upon  this  are  placed  the  wheels  upon  which  the  whole 
building  turns.  The  wheels  are  eight  in  number,  of  cast- 


ASTRONOMICAL   OBSERVATORIES.  271 

iron,  and  grooved.  The  circular  iron  rail  attached  to 
the  lower  part  of  the  building  traverses  the  uppen 
surface  of  the  wheels  one  foot  from  the  floor.  The  roof 
is  of  tin,  and  conical ;  the  aperture  is  16  inches  wide, 
and  is  covered  by  a  door  which  opens  in  a  single  piece. 
The  pier  upon  which  the  telescope  rests  is  built  of  stone 
faced  with  brick,  and  rises  two  feet  above  the  floor. 

The  telescope  is  a  refractor,  made  by  Henry  Fitz. 
The  object-glass  has  an  aperture  of  six  and  a  half  inches, 
and  a  focal  length  of  eight  feet;  and  it  was  mounted 
on  an  equatorial  stand  by  Phelps  and  Ghirley.  The 
declination  circle  has  a  diameter  of  ten  inches,  and 
reads  by  verniers  to  one  minute  of  arc ;  the  hour  circle 
has  a  diameter  of  seven  inches,  and  reads  by  verniers 
to  six  seconds  of  time.  The  telescope  is  driven  by 
clock-work,  and  cost  $1,125. 

The  object-glass  of  this  telescope  has  given  entire 
satisfaction.  Saturn  is  seen  with  a  division  in  the  outer 
ring,  the  division  being  somewhat  eccentrical  and  nearer 
the  outer  edge.  Occasionally  there  has  been  seen  a  sub- 
division of  the  inner  bright  ring  at  the  ansae,  near  the 
inner  edge.  The  interior  dark  ring  is  also  seen. 

The  planet  Mars  is  well  defined  in  a  good  atmos- 
phere with  a  white  circumference,  both  at  the  equatorial 
and  the  polar  regions,  the  interior  space  being  varied 
with  dark  shades. 

The  comet-seeker  was  also  made  by  Henry  Fitz. 
The  object-glass  has  an  aperture  of  four  inches,  and  is 
fitted  to  a  section  of  tube  which  screws  into  the  finder 


272  HISTORY   OF  ASTRONOMY. 

of  the  telescope.  This  mode  lias  the  advantage  of  a 
ready  reference  to  the  larger  instrument,  but  is  somewhat 
inconvenient  from  the  interference*  of  the  stand  in  ob- 
serving the  space  beneath  the  pole  and  near  the 
meridian. 

Three  comets  have  been  independently  discovered  by 
Mr.  Yan  Arsdale,  viz.,  one  November  25,  1853,  another 
June  24,  1854,  and  a  third  September  13,  1854.  The 
first  of  these  was  not  seen  in  Europe  until  December  2, 
a  week  after  it  was  discovered  by  Mr.  Yan  Arsdale; 
the  second  was  discovered  in  Europe  June  4 ;  the  third 
was  discovered  at  Berlin,  September  12.  These  dis- 
coveries were  made  while  searching  for  comets,  although 
the  search  was  not  thorough,  as  the  view  near  the 
horizon  is  obstructed  by  buildings,  and  the  examination 
was  seldom  continued  to  a  late  hour. 

SHELBY  COLLEGE  OBSERVATORY. 

A  very  superior  telescope  was  ordered  in  1848  from 
the  establishment  of  Merz  and  Mahler,  of  Munich,  for 
the  use  of  Shelby  College,  Shelbyville,  Kentucky.  It 
has  an  aperture  of  seven  and  a  half  inches,  and  a  focal 
length  of  ten  feet.  The  mounting  is  admirably  exe- 
cuted, and  differs  in  some  respects  from  any  other  in 
this  country.  It  is  furnished  with  a  filar  and  an  annular 
micrometer.  The  filar  micrometer  has  six  positive  eye- 
pieces, with  powers  from  100  to  570.  There  are  also  5 
negative  eye-pieces,  magnifying  from  102  to  550  times. 
The  hour  circle  is  10  inches  in  diameter,  reading  to  4 


ASTRONOMICAL  OBSERVATORIES.  273 

seconds  of  time ;  the  declination  circle  is  15  inches  in 
diameter,  reading  to  10  seconds  of  arc.  This  instrument 
was  received  in  November,  1850,  and  cost  $3,500. 

* 

This*telescope  was  mounted  on  the  top  of  the  college 
building,  about  50  feet  from  the  ground,  under  a  revolv- 
ing dome  18  feet  in  diameter,  and  was  supported  by  a 
heavy  cast-iron  tripod,  whose  legs  consist  of  hollow  iron 
columns,  each  weighing  about  600  pounds,  passing 
through  three  floors  of  the  building,  and  resting  on  solid 
masonry  below  the  lower  floor.  The  dome  revolves  on 
cannon-balls,  and  is  turned  by  wheels  gearing  into  a  circle 
of  cogs  on  the  wall  below  the  dome.  The  time  is  fur- 
nished by  a  box  chronometer. 

The  cost  of  the  telescope  and  observatory  was  defrayed 
partly  by  subscription;  but  the  greater  part  of  the  ex- 
pense was  borne  by  the  president  of  the  institution,  the 
Rev.  William  J.  Walker. 

BUFFALO  OBSERVATORY. 

This  observatory  is  the  property  of  Mr.  William  S.  Van 
Duzee.  It  was  erected  in  the  summer  of  1851,  and  the 
instruments  mounted  in  the  following  winter.  The 
building  is  24  by  25  feet  square,  having  two  piers,  one 
for  the  transit,  and  the  other  for  the  equatorial  instru- 
ment, resting  on  a  foundation  of  solid  masonry,  ex- 
tending twelve  feet  below  the  surface  of  the  earth,  and 
surrounded  by  a  wall  two  feet  distant  from  this 
foundation,  so  that  no  motion  may  be  felt  by  the 
passing  of  carriages. 

12* 


274  HISTORY  OF  ASTRONOMY. 

The  central  pier  is  built  of  brick,  and  is  8  feet  square 
through  the  first  story,  which  is  15  feet  high,  but  through 
the  second  story  is  only  6  feet  square.  This  pier  is  sur- 
mounted by  a  traveling  dome,  17  feet  in  diameteif  and  is 
pierced  by  an  opening  2  feet  wide,  extending  from  a 
point  4  feet  above  the  floor  to  8  inches  on  the  opposite 
side  of  the  zenith.  The  dome  rests  on  twelve  eighteen- 
pound  balls,  which  turn  between  two  cast-iron  annular 
grooves. 

The  transit  pier  is  five  feet  square,  and  extends  three 
feet  into  the  second  story.  The  meridian  observing  slits 
are  made  two  feet  in  the  clear,  and  afford  an  uninter- 
rupted view  of  the  meridian  from  the  northern  to  the 
southern  point  of  the  horizon.  Both  piers  are  covered 
with  marble  slabs,  three  inches  thick. 

The  equatorial  telescope,  which  is  erected  under  the 
dome,  was  made  by  Henry  Fitz,  of  New  York.  It  is  a 
refractor  of  11  feet  focus  and  9  inches  aperture  ;  and  has 
a  position  micrometer  furnished  with  an  illuminating  ap- 
paratus. The  hour  circle  is  12  inches  in  diameter,  and 
the  declination  circle  15  inches,  each  reading  by  two 
verniers.  The  telescope  is  moved  by  clock-work,  so 
that  the  object  under  examination  may  be  kept  steadily 
in  the  center  of  the  field.  This  telescope  is  furnished 
with  ten  eye-pieces,  the  highest  magnifying  800  times. 

The  transit  instrument  is  in  the  second  story,  has  a 
clear  aperture  of  2  inches,  and  a  focal  length  of  33 
inches.  Near  the  transit  is  the  clock  with  a  mercurial 
pendulum. 


ASTRONOMICAL  OBSERVATORIES.  275 

MR,  CAMPBELL'S  OBSERYATORT,  NEW  YORK. 

This  observatory  is  built  on  the  top  of  Mr.  Campbell's 
dwelling-house  in  New  York  city,  in  Sixteenth-street, 
near  the  Fifth  Avenue,  and  Was  completed  in  1852.  The. 
house  is  30  feet  wide  and  four  stories  high.  The  hall  is 
10  feet  wide,  and  the  partition  wall  which  separates  the 
hall  from  the  rest  of  the  house  is  of  brick,  and  extends  to 
the  roof.  This  and  the  adjoining  gable  were  raised  so  as 
to  make  another  story  over  that  part  of  the  house,  and  a 
room  was  thus  obtained  10  feet  wide  and  35  feet  long. 
Twelve  feet  at  one  end  are  appropriated  for  the  dome  and 
telescope.  The  observatory  is  furred  off  so  as  to  make 
an  octagon  of  12  feet  in  diameter ;  and  at  the  height  of  5 
feet,  the  octagon  is  changed  into  a  circle  to  support  the 
wooden  curb-  which  constitutes  the  bed-plate  of  the  dome. 
Upon  the  bed-plate  is  placed  a  circular  rail,  12  feet  in 
diameter  on  the  inside,  3  inches  wide,  and  having  a  raised 
bead  upon  the  upper  surface. 

The  dome  is  12  feet  in  diameter,  the  base  being  a  coun- 
terpart of  the  curb,  which  constitutes  the  bed-plate.  The 
aperture  for  the  telescope  is  15  inches  wide,  and  extends 
a  little  beyond  the  zenith.  It  is  closed  with  a  sliding 
door,  which  is  made  so  that  it  may  slip  over  the  zenith  to 
the  opposite  side  of  the  dome,  and  this  motion  is  effected 
by  turning  a  crank.  The  dome  revolves  upon  seven 
wheels  of  four  inches  diameter,  in  which  grooves  are 
turned  to  correspond  with  the  bead  on  the  iron  rail.  The 
shaft  of  one  of  these  wheels,  is  made  long  enough  to  re- 


276  HISTOKY   OF   ASTRONOMY. 

ceive  a  pinion  at  one  end  and  a  handle  at  the  other.  The 
pinion  fits  a  rack  which  encircles  the  rail;  while  the 
handle  and  also  the  operator  move  round  with  the  dome, 
which  is  accomplished  by  the  peculiar  construction  of  the 
observer's  seat.  This  is  a  Small  flight  of  stairs,  having 
an  angle  of  elevation  suited  to  the  sweep  of  the  eye-piece, 
so  that  each  step  makes  a  convenient  seat.  The  frame  is 
of  wrought  iron ;  the  string  pieces  are  secured  to  the  base 
of  the  dome,  and  the  bottom  of  the  stairs  rests  upon  two 
wheels,  in  which  grooves  are  made  to  fit  a  circular  iron 
rail  which  is  secured  to  the  floor.  A  circular  table  is 
substituted  for  the  ordinary  reading  steps.  It  is  sup- 
ported upon  legs,  with  rollers,  and  is  secured  at  each  end 
to  the  bottom  steps  of  the  observer's  seat  so  as  to  revolve 
with  it- 
Three  stout  beams  rest  upon  the  brick  walls  across  the 
center  of  the  octagon,  making  a  support  for  the  pedestal 
of  the  telescope.  This  pedestal  is  a  drum  of  boiler  iron, 
three  feet  in  diameter,  and  the  same  in  -height.  It  is  lined 
with  brick  like  a  well,  and  covered  with  a  smooth,  round 
flag-stone,  projecting  an  inch  over  the  iron.  The  mahog- 
any frame  of  the  telescope,  having  four  feet  with  adjust- 
ing screws,  stands  upon  this  stone. 

The  telescope  is  an  achromatic  refractor  of  eight  inches 
aperture,  and  ten  and  a  half  feet  focal  length,  made  by 
Henry  Fitz.  It  has  six  negative  eye^pieces,  magnifying 
from  60  to  480  times.  The  stand  is  made  of  cast  iron, 
excepting  the  circles,  which  are  of  brass ;  and  a  clock  is 
attached  to  the  telescope  for  keeping  the  object  in  the 


ASTRONOMICAL  OBSERVATORIES.  277 

field  of  view.  The  thread  which  fits  the  tangent  screw  is 
cut  in  the  edge  of  the  ring,  detached  from  the  hour  circle, 
and  pressed  against  it  by  the  elasticity  of  a  thin  brass 
plate,  which  is  secured  by  screws  so  as  to  give  the  re- 
quisite friction.  This  arrangement  permits  the  telescope 
to  be  moved  in  any  direction,  even  while  connected  with 
the  clock,  and  obviates  the  necessity  of  clamping  and  un- 
clamping. 

The  solar  eclipse  of  May  26,  1854,  was  carefully  ob- 
served by  this  telescope,  and  a  series  of  daguerreotypes 
(28  in  number)  were  taken  at  intervals  of  about  five 
minutes,  showing  the  progress  of  the  eclipse  in  a  novel 
and  beautiful  manner.  These  images,  which  are  two 
inches  in  diameter,  are  extremely  well  defined,  and  serve 
as  permanent  registers  of  the  transient  phenomena  of  the 
eclipse. 

OBSERVATORY  OF  MICHIGAN  UNIVERSITY. 

Soon  after  the  Rev.  Dr.  Tappan  was  elected  Chancellor 
of  Michigan  University,  in  1852,  he  conceived  the  idea 
of  establishing  an  astronomical  observatory  in  connection 
with  the  university.  During  the  succeeding  winter  the 
claims  of  this  object  were  laid  before  the  citizens  of  De- 
troit, and  they  responded  to  the  appeal  in  a  prompt  and 
liberal  manner.  The  sum  of  ten  thousand  dollars  was 
almost  immediately  pledged  for  this  object,  and  an  ad- 
ditional sum  was  promised  if  it  should  be  found  necessary. 

The  foundations  of  the  building  were  laid  in  the  sum- 
mer of  1853,  and  the  observatory  was  completed  in  the 


278 


HISTORY   OF   ASTRONOMY. 


autumn  of  1854.  In  February,  1853,  a  large  equatorial 
telescope  was  ordered  from  Henry  Fitz,  of  New  York ; 
and  during  the  summer  of  the  same  year,  a  meridian 
circle  was  ordered  from  Berlia  The  main  building  for 
the  observatory  is  32  feet  square,  and  it  is  surmounted  by 
a  hemispherical  dome,  23  feet  in  diameter.  The  dome 


OB8ERVATOBY   OF   MICHIGAN   "UNIVERSITY. 


has  an  opening  32  inches  wide,  extending  from  near  its 
base  to  the  zenith,  and  the  opening  is  closed  by  a  single 
curved  shutter,  which  slides  in  a  groove,  so  that  it  may 
be  made  to  travel  over  to  the  opposite  side  of  the  dome. 
A  pier,  whose  foundations  are  laid  ten  feet  beneath  the 
surface  of  the  earth,  rises  through  the  center  of  the  build- 
ing to  the  height  of  20  feet  from  the  ground,  and  upon 
this  rests  the  great  equatorial.  On  the  east  and  west 


279 

sides  of  the  central  building  are  wings  28  feet  by  19 ;  the 
east  wing  being  appropriated  to  the  meridian  circle,  and 
the  west  wing  being  appropriated  for  the  apartments  of 
the  astronomer.  The  cost  of  the  entire  building  has  been 
about  $7000. 

The  meridian  circle  was  made  by  Pistor  and  Martins, 
of  Berlin.  It  has  a  telescope  of  eight  feet  focal  length, 
and  has  two  graduated  circles  of  three  feet  diameter,  each 
of  which  is  read  by  four  microscopes.  There  are  also 
two  small  circles,  with  levels  near  the  eye-piece  for  set- 
ting the  instrument  to  the  proper  altitude.  The  eight 
microscopes  are  illuminated  by  two  stationary  lamps, 
which  stand  on  the  brass  columns  which  support  the 
counterpoises.  The  illumination  of  the  wires  can  be  so 
regulated  as  to  present  either  a  bright  field  with  dark 
Jines,  or  a  dark  field  with  bright  lines.  Two  collimators 
are  mounted  on  the  north  and  south  of  the  meridian  circle, 
and  there  are  conveniences  for  observing  stars,  as  well  as 
the  nadir  point,  by  reflection  from  a  basin  of  mercury. 
The  circle,  with  the  collimators,  cost  $3300,  and  this  sum 
was  contributed  by  H.  N.  Walker,  Esq.,  of  Detroit.  The 
clock  was  made  by  M.  Tiede,  of  Berlin.  It  has  a  pen- 
dulum with  a  steel  and  zinc  compensation,  and  cost  $300. 

The  great  equatorial  telescope  was  made  by  Mr.  Fitz, 
of  New  York.  The  object-glass  has  a  clear  aperture  of 
twelve  and  a  half  inches,  and  a  focal  length  of  seventeen 
feet.  It  has  seven  negative  and  six  positive  eye-pieces, 
the  highest  magnifying  power  being  1200.  The  circles 
are  each  twenty  inches  in  diameter,  the  hour  circle  read- 


280  HISTORY   OF  ASTRONOMY. 

ing  to  two  seconds  of  time,  and  the  declination  circle  to 
twenty  seconds  of  arc.  It  is  also  furnished  with  clock- 
work and  micrometer.  iThe  crown-glass  was  obtained 
from  Bontemps,  of  Birmingham,  England,  and  the  flint- 
glass  was  obtained  from  Paris.  The  price  of  this  tele- 
scope was  $6000,  and  its  performance  has  proved  entirely 
satisfactory.  The  entire  cost  of  the  building  and  instru- 
ments was  about  $17,000. 

Dr.  F.  Briinnow,  an  astronomer  well  known  by  his 
observations  while  connected  with  the  observatory  of 
Berlin,  and  also  by  his  Treatise  on  Spherical  Astronomy, 
has  been  appointed  director  of  this  observatory,  and  has 
already  entered  upon  his  duties.  We  congratulate  the 
University  of  Michigan  in  having  secured  the  services  of 
so  skillful  and  learned  an  astronomer  ;  and  we  anticipate 
that  the  career  of  Dr.  Briinnow  will  shed  luster  upon 
his  adopted  country,  while  he  contributes  to  the  promo- 
tion of  that  science  to  which  his  life  has  been  devoted. 

CLOYERDEN  OBSERVATORY,  CAMBRIDGE,  MASSACHUSETTS. 

The  great  telescope  belonging  to  Shelby  College  was 
temporarily  loaned  to  Professor  Joseph  Winlock,  and 
was  removed  to  Cambridge,  Massachusetts,  where  tem- 
porary accommodations  were  provided  for  it,  and  this 
establishment  is  known  by  the  name  of  Cloverden  Ob- 
servatory. This  consists  of  a  circular  wooden  building, 
with  a  revolving  dome,  fifteen  feet  in  diameter,  and  a 
small  adjoining  room  for  other  instruments.  The  dome 
is  very  light,  consisting  of  a  wooden  frame  covered  with 


ASTRONOMICAL  OBSERVATORIES. 


281 


tarpaulin,  and  revolves  on  wooden  balls  with  so  little  re- 
sistance, that  it  is  easily  pushed  round  with  the  hand 
without  wheels  or  levers.  In  the  adjoining  apartment 
is  a  four-feet  transit  and  several  chronometers.  The 
standard  chronometer  was  made  by  Kessels. 

Numerous  observations  on  comets,  and  some  of  the 
newly  discovered  planets,  have  been  made  with  this 
telescope  by  Dr.  B.  A.  Gould  and  Professor  Joseph 
Winlock,  some  of  which  have  been  published  in 
"  Gould's  Astronomical  Journal."  The  great  telescope 
has  recently  been  returned  to  Shelby  College. 

DUDLEY  OBSERVATORY,  AT  ALBANY. 


About  three  years  since,  it  was  proposed  to  establish 
at  Albany  a  university,  comprehending  a  series  of  prac- 
tical, professional,  and  scientific  schools.  As  a  part  of 
this  enterprise,  it  was  resolved  to  establish  an  as- 
tronomical observatory,  the  charge  of  which  Professor 
O.  M.  Mitchell  had  already  signified  his  willingness  to 


282  HISTORY  OF  ASTRONOMY. 

accept/  General  Steven  Yan  Kensselaer  kindly  offered 
a  donation  of  several  acres  of  land  near  the  northern 
-limit  of  the  city,  affording  an  excellent  site  for  the 
contemplated  building.  Mrs.  Blandina  Dudley,  a  lady 
distinguished  for  her  wealth  and  liberal  spirit,  gave 
toward  the  building  the  sum  of  $13,000.  ContributiQns 
were  received  from  several  gentlemen  of  the  city,  in- 
creasing this  sum  to  $25,000.  The  building  was  com- 
menced in  the  spring  of  1853,  upon  a  plan  designed  by 
Professor  Mitchell,  and  the  late  Sears  C.  Walker,  and 
was  erected  under  the  supervision  of  Professor  Perkins. 

The  ground-plan  of  the  building  is  in  the  form  of  a 
cross,  84  feet  in  front  by  72  feet  in  depth.  The  central 
room  is  28  feet  square ;  the  east  and  west  wings,  which 
are  designed  for  the  use  of* the  meridian  instruments,  are 
each  23  feet  square,  and  provided  with  the  usual  open- 
ings in  the  meridian.  The  north  wing  is  40  feet  square, 
divided  into  a  library  room,  two  computing  rooms, 'and 
other  small  rooms  for  the  magnetic  apparatus  for  re- 
cording the  observations.  The  equatorial  room,  which 
is  in  the  second  story,  is  of  a  circular  form,  28  feet  in 
diameter,  the  tower  revolving  upon  iron  balls. 

The  main  pier  for  the  support  of  the  equatorial  was 
commenced  six  feet  below  the  bottom  of  the  cellar, 
with  its  base,  15  feet  square,  resting  on  a  bed  of  con- 
crete and  rubble  16  inches  in  thickness.  The  size  of 
the  pier  was  gradually  reduced  to  10  feet  square  at  the 
level  of  the  cellar,  and  thus  continued  upward  without 
further  variation.  The  whole  is  built  in  the  most  sub- 


ASTRONOMICAL  OBSERVATORIES.  283 

stantial  manner  of  large  stone,  well  bedded.  The  piers 
in  the  transit  rooms  are  six  feet  by  eight,  and  each  room 
is  furnished  with  clock  piers  of  similar  construction. 
The  walls  "are  of  brick ;  but  the  basement,  portico,  cor- 
nices, etc.,  are  of  dressed  freestone.  The  library  and 
commuting  rooms  are  warmed  by  heated  air  from  a  base- 
ment furnace.  These  rooms  and  the  staircase  are  all 
accessible  from  the  vestibule.  A  bust  of  the  late 
Charles  Dudley,  executed  by  E.  D.  Palmer,  an  artist  of 
Albany,  is  to  be  placed  near  the  principal  entrance. 

The  Dudley  observatory  was  incorporated  in  1853, 
and  its  management  is  vested  in  a  board  of  trustees. 
In  the  summer  of  1855,  Mrs.  Dudley  offered  to  furnish 
the  requisite  means  for  procuring  a  heliometer  of  the 
largest  dimensions.  The  construction  of  this  instru- 
ment has  been  entrusted  to  Mr.  Charles  A.  Spencer, 
who  proposes  to  make  a  telescope  with  an  object-glass 
of  10  inches  aperture.  The  price  of  this  instrument  is 
to  be  $14,500.  A  gentleman  of  Albany  contributed 
$5000  for  a  meridian  circle,  and  this  instrument  has 
been  ordered  from  Pistor  and  Martins,  of  Berlin.  An- 
other gentleman  of  Albany  contributed  $1000  for  an 
astronomical  clock.  The  transit  instrument  will  be 
furnished  by  the  U.  S.  Coast  Survey,  and  will  cost 
$1.500.  It  is  expected  that  the  observatory  will  soon 
commence  active  operations  under  the  direction  of  Dr. 
B.  A.  Gould. 


284 


HISTORY  OF  ASTRONOMY. 


HAMILTON  COLLEGE    OBSERYATORT. 

In  1852  and  1853,  Professor  Charles  A  very  raised 
$15,000  by  subscription,  mostly  in  small  sums,  for  the 
purpose  of  procuring  a  large  telescope  of  American 

manufacture.     It  was  then    determined  to  erect  on  the 

» 

grounds  of  Hamilton  College  a  building  suitable  for  an 
astronomical  observatory,  and  to  furnish  it  with  first-class 


HAMILTON   COLLEGE  OBSEEVATOKY. 


instruments.  In  the  spring  of  1854,  Mr.  A.  J.  Lathrop, 
of  Utica,  presented  plans  of  a  building,  which  were 
approved,  and  the  building  was  erected  the  same  year. 

The  observatory  consists  of  a  central  building,  with 
wings  on  the  east  and  west  sides.  The  main  building 
is  27  feet  square,  and  two  stories  high,  surmounted  by  a 


ASTRONOMICAL   OBSERVATORIES. 


285 


tower,  20  feet  in  diameter,  which  revolves  on  eight  cast- 
iron  balls  upon  an  iron  track.  The  wings  are  each 
18  feet  square.  The  east  wing  is  designed  for  a  com- 
puting room;  the  west  wing  is  designed  for  a  transit 
room,  and  it  commands  a  fine  meridian.  The  transit 
pier-  is  built  of  limestone.  It  descends  six  feet  below  the 


HA3ULTOX   COLLEGE  TELESCOPE. 


surface  of  the  ground,  and  is  eight  feet  by  five  at  the 
top.  In  the  center  of  the  main  building  is  the  large 
pier,  built  also  of  limestone.  It  descends  six  feet  below 
the  surface  of  the  ground,  is  ten  feet  square  at  the  base, 


286  HISTORY  OF  ASTRONOMY. 

and  seven  feet  square  at  the  top,  and  is  entirely  detached 
from  the  building.  On  the  pier  rests  a  granite  block, 
fourteen  feet  high,  to  which  the  great  refractor  is  to  be 
attached.  The  observatory  building  cost  $5000. 

A  refracting  telescope  was  ordered  from  Messrs. 
Spencer  and  Eaton,  of  Canastota,  New  York,  and 
has  recently  been  completed.  The  object-glass  has  a 
diameter  of  13£  inches,  with  a  focal  length  of  16  feet. 
The  hour  circle,  divided  on  silver,  has  a  diameter  of 
15  inches,  and  reads  by  two  verniers  to  two  seconds  of 
time.  The  declination  circle  has  a  diameter  of  26 
inches,  and  reads  to  four  seconds  of  arc.  The  filar 
micrometer  has  eye-pieces  made  of  double  achromatics, 
instead  of  the  usual  Kamsden  form,  giving  magnifying 
powers  from  100  to  1000.  The  negative  eye-pieces  give 
magnifying  powers  from  80  to  1500  times.  The  usual 
sidereal  motion  is  given  by  clock-work. 

The  focal  length  of  this  telescope  is  about  four  feet 
less  than  is  usual  in  the  Munich  instruments  of  the  same 
aperture.  The  telescope  is  thus  rendered  less  unwieldy, 
and  in  the  opinion  of  Mr.  Spencer,  its  optical  performance 
is  not  impaired.  The  flint  and  crown  discs  for  this 
instrument  were  procured  through  the  agents,  Messrs. 
Cook,  Beckel  and  Co.,  New  York,  from  Joseph  Bader,  of 
Kohlgrub,  and  have  been  found  to  be  remarkably  exempt 
from  striaB.  The  object-glass  has  been  subjected  to  par- 
tial trial  with  very  satisfactory  results.  The  price  of  this 
telescope  was  $10,000.  The  transit  instrument  and  clock 
have  not  yet  been  ordered. 


ASTKONOMICAL  OBSEBVATOKIES.  287 

From  the  preceding  sketch  it  must  be  apparent  that 
within  a  few  years,  rapid  progress  has  been  made 
toward  supplying  our  country  with  the  means  of 
making  astronomical  observations.  We  now  have  in- 
struments which  permit  us  to  engage  in  astronomical 
researches  upon  a  footing  of  equality  with  the  oldest 
establishments  of  Europe,  while  the  number  of  observers 
and  the  taste  for  astronomical  studies  has  kept  pace  with 
the  increase  of  our  instruments.  The  importance  of 
astronomical  observations  is  beginning  to  be  generally 
appreciated  ;  but  for  the  benefit  of  those  whose  attention 
has  not  been  particularly  turned  to  this  subject,  a  few 
suggestions  are  added. 

An  astronomical  observatory  may  be  made  useful  in 
almost  any  locality,  but  it  may  be  rendered  especially 
valuable  in  the  neighborhood  of  a  large  commercial  em- 
porium. The  following  may  be  enumerated  among  these 
advantages : 

I.  It  furnishes  an  accurate  determination  of  time,  which 
is  a  matter  of  importance  to  almost  every  citizen,  but 
more  especially  to  certain  classes  of  the  community. 
Every  vessel  which  puts  to  sea,  carries  with  it  one  or 
more  chronometers,  and  the  chronometer  is  almost  ex- 
clusively relied  upon  to  furnish  the  longitude  of  the 
vessel  from  day  to  day.  An  error  of  a  few  seconds  in 
the  chronometer  causes  a  corresponding  error  in  the  lon- 
gitude deduced,  and  such  errors  have  been  the  occasion 
of  the  loss  of  numerous  vessels.  It  is,  therefore,  a  matter 
of  vital  importance  that  the  error  and  rate  of  all  chro- 


288  HISTORY   OF  ASTRONOMY. 

nometers  which  are  carried  to  sea  should  be  determined 
with  the  utmost  precision.  In  every  commercial  city 
there  are  private  establishments  where  this  duty  is  reg- 
ularly attended  to.  A  public  observatory  does  not 
necessarily  interfere  with  these  private  establishments, 
but  affords  the  means  of  rendering  them  more  accurate 
and  efficient.  How  this  may  be  accomplished  will 
presently  be  shown. 

An  exact  knowledge  of  time  is  also  of  vital  importance 
to  the  conductors  of  all  railroad  trains.  A  small  error  in 
a  conductor's  watch  has  repeatedly  been  the  occasion  of 
the  collision  of  railroad  trains,  and  the  consequent  de- 
struction of  human  life.  Many  of  the  railroad  companies 
in  this  country  incur  annually  considerable  expense  to 
provide  all  the  conductors  with  correct  time. 

An  accurate  knowledge  of  time  is  important  to  all 
business  men,  but  especially  to  banking  and  other  houses 
where  business  is  entirely  suspended  at  a  fixed  hour  of 
the  day.  A  small  mistake  in  the  time  might  occasion 
not  only  serious  disappointment,  but  also  pecuniary  loss. 

An  astronomical  observatory  is  furnished  with  clocks 
of  the  best  construction,  and  with  transit  instruments  for 
determining  daily  the  error  of  these  clocks.  The  observ- 
atory, therefore,  can  furnish  time  with  all  the  precision 
which  can  be  desired ;  but  to  render  this  knowledge  con- 
veniently accessible  to  the  public,  requires  some  peculiar 
arrangements.  The  following  is  the  arrangement  for  this 
purpose  which  existed  for  many  years  at  Greenwich  ob- 
servatory :  On  one  of  the  turrets  of  the  observatory  is 


ASTRONOMICAL  OBSERVATORIES.  289 

erected  a  mast,  upon  which  slides  a  ball,  five  feet  in 
diameter,  consisting  of  a  frame  of  wood  covered  with 
leather.  A  little  before  one  o'clock  every  day  the  ball  is 
slid  up  to  the  top  of  the  mast,  where  it  is  held  by  in- 
geniously contrived  machinery.  Precisely  at  one  o'clock 
an  assistant,  who  is  specially  charged  with  this  duty, 
presses  a  spring,  and  the  ball  instantly  descends.  By  this 
means  all  persons  in  sight  of  the  ball  are  enabled  daily  to 
test  the  accuracy  of  their  clocks.  At  the  Washington 
observatory  a  ball  of  smaller  size  than  that  at  Greenwich 
is  elevated  every  day  on  a  flag-staff,  and  is  lowered  at  the 
precise  instant  of  twelve  o'clock. 

Within  the  last  two  years  the  arrangements  at  Green- 
wich for  furnishing  the  public  with  an  accurate  knowl- 
edge of  the  time  have  been  very  much  improved.  A 
normal  clock  is  furnished  with  a  small  apparatus,  by 
means  of  which,  whenever  its  error  is  determined  by 
observations,  its  indications  can  be  rendered  perfectly 
correct.  This  clock  keeps  in  motion  a  sympathetic  gal- 
vanic clock  at  the  entrance-gate  of  the  observatory,  and 
also  a  clock  at  the  terminus  of  the  South-eastern  Railway. 
It  sends  galvanic  signals  every  day  along  all  the  principal 
railways  diverging  from  London ;  it  drops  the  Greenwich 
ball  and  the  ball  on  the  offices  of  the  Electric  Telegraph 
Company  in  the  Strand.  The  Lords  Commissioners  of 
the  Admiralty  have  also  erected  a  time  signal-ball  at 
Deal,  for  the  use  of  the  shipping  in  the  Downs,  which  is 
dropped  every  day  by  a  galvanic  current  from  the  Royal 
observatory. 

13 


290  HISTORY   OF  ASTRONOMY. 

Similar  arrangements  might  be  adopted  in  every  large 
commercial  city.  If,  for  example,  there  was  a  public  ob- 
servatory in  the  neighborhood  of  New  York,  a  clock  at 
the  observatory  might  be  made  every  day,  by  means  of 
an  electric  current,  to  drop  a  time-ball  on  the  Merchants7 
Exchange  or  the  City  Hall,  another  on  Brooklyn  Heights, 
another  on  Staten  Island,  and  another  at  Sandy  Hook ; 
as  well  as  at  any  other  point  where  public  convenience 
might  require.  It  might  also  maintain  in  motion  a 
sympathetic  galvanic  clock  at  the  City  Hall,  at  the 
Custom-house,  at  the  Exchange,  and  at  every  railway 
station  in  the  city — a  clock  which  should  never  differ  by 
an  appreciable  quantity  from  perfectly  accurate  time. 
Such  a  system  would  contribute  not  a  little  to  the  security 
of  commerce  and  the  punctuality  of  business.* 

II.  A  second  advantage  to  be  derived  from  an  astro- 
nomical observatory  is  that,  by  extending  our  knowledge 
of  the  heavenly  bodies,  it .  directly  contributes  to  the  se- 
curity of  commerce.  The  prosperity  of  commerce  depends 
entirely  upon  the  safety  with  which  the  ocean  can  t>e 
navigated,  and  this  depends  upon  the  accuracy  with 
which  a  ship's  place  can  be  determined  from  day  to  day. 
Had  it  not  been  for  the  labors  of  modern  astronomers  in 
their  observatories,  vessels  would  still,  as  in  ancient 
times,  creep  timidly  along  the  coast,  afraid  to  venture  out 
of  sight  of  land ;  or  if  they  were  compelled  to  venture 

*  Since  the  preceding  was  written,  the  officers  of  the  Dudley  observ- 
atory at  Albany  have  offered  to  furnish  time  for  the  city  of  New  York, 
substantially  in  the  manner  above  suggested. 


ASTRONOMICAL  OBSERVATORIES.  291 

into  the  open  ocean,  they  would  be  exposed  to  imminent 
danger  in  approaching  land,  not  knowing  how  far  distant 
the  port  might  be.  The  loss  of  time  resulting  from  pur- 
suing this  timid  course,  and  the  numerous  disasters  which 
could  not  be  avoided,  would  more  than  double  the  ex- 
pense of  maintaining  our  foreign  commerce.  Astrono- 
mers, by  their  accurate  determinations  of  the  places  of 
the  sun,  the  moon,  and  the  stars,  have  given  prosperity 
to  commerce  and  boundless  wealth  to  our  commercial 
cities.  But  there  is  still  much  for  astronomers  to  do 
The  places  of  the  heavenly  bodies  even  at  present  are  not 
known  with  all  the  precision  which  is  desired.  Great 
errors  in  determining  a  ship's  place  are  now  of  rare 
occurrence ;  but  small  errors  frequently  lead  to  disastrous 
consequences,  and  it  is  therefore  important  to  reduce  the 
errors  to  the  least  possible  amount. 

III.  An  astronomical  observatory,  well  equipped,  be- 
comes a  center  of  influence  which  is  felt  on  all  the  educa- 
• 

tional  establishments  of  the  country,  even  those  of  the 
humblest  grade.  It  is"  impossible  to  maintain  common 
schools  in  a  state  of  efficiency  without  institutions  of  a 
higher  grade,  corresponding  to  our  academies,  which 
shall  furnish  teachers  for  the  elementary  schools,  and  also 
afford  encouragement  to  ambitious  scholars,  who  wish  to 
extend  their  studies  beyond  the  elementary  branches. 
The  academies  can  not  be  maintained  in  a  flourishing 
condition  without  institutions  of  a  higher  grade,  corre- 
sponding to  our  colleges,  where  teachers  are  educated  for 
the  academies,  and  where  ambitious  students  from  the 


292  HISTORY  OF  ASTRONOMY. 

academies  may  extend  still  further  the  range  of  their 
studies.  College  professors,  in  their  turn,  are  in  danger 
i  sf  of  settling  down  into  mere  retailers  of  other  men's  ideas, 
M  \  without  aspiring  to  add  any  thing  to  the  stock  of  human 
knowledge,  unless  they  are  surrounded  by  institutions 
whose  leading  object  is  the  increase  of  knowledge.  An 
astronomical  observatory,  therefore,  is  a  center  of  genial 
influence,  which  directly  or  indirectly  imparts  life  and 
efficiency  to  all  the  subordinate  institutions  of  education. 
It  is  also  a  place  where  men  of  business  may  acquire  new 
ideas  of  the  wonders  of  the  material  universe ;  where  men, 
whose  days  are  spent  in  toiling  for  the  acquisition  of 
wealth,  may  learn  that  there  are  mines  of  intellectual 
riches  more  inexhaustible  than  the  mines  of  California. 
Men  who  from  morning  to  night  are  engaged  in  the 
duties  of  an  arduous  profession,  or  in  the  labors  of  the 
counting-house  or  exchange,  often  feel  the  need  of  recrea- 
tion when  the  hours  of  business  are  over.  What  mode 
of  recreation  is  more  rational — what  is  better  fitted  to  in- 
spire the  mind  with  noble  sentiments — than  to  direct  the 
thoughts  to  the  wonders  of  the  material  universe,  to  the 
vastness  of  the  visible  creation,  as  exhibited  to  the 
eye  of  an  astronomer  with  the  assistance  of  the  tele- 
scope ? 


SECTION   II. 

ASTRONOMICAL  EXPEDITION  TO  CHILI  DURING  THE  YEARS 
1849—1852. 

IN  the  year  1847,  Dr.  C.  L.  Grerling,  a  distinguished 
mathematician  of  the  Marburgh  University,  suggested 
the  importance  of  a  new  determination  of  the  sun's 
parallax  by  observations  upon  Yenus  at  and  near  her 
stationary  periods.  The  determination  of  the  dimensions 
of  the  solar  system  rests  entirely  upon  the  assumed 
value  of  the  sun's  parallax.  The  value  now  generally 
received,  viz.,  8*.57,  rests  upon  the  observations  of  the 
transit  of  Yenus  in  1769.  Transits  of  Yenus  over  the 
sun's  disc  afford  the  best  method  of  determining  this 
parallax;  but  these  phenomena  are  of  very  rare  oc- 
currence, there  being  not  a  single  transit  visible  in  any 
part  of  the  world  from  1769  to  1874.  Now,  although 
the  observations  of  the  transit  of  1769  are  believed  to 
have  afforded  a  very  accurate  value  of  the  sun's  parallax, 
yet  it  is  much  to  be  regretted  that  the  results  obtained 
by  combining  the  observations  at  different  stations  two 
and  two,  differ  among  themselves  by  an  entire  second. 
It  is  therefore  very  desirable  that  this  result  should  be 
verified  by  independent  methods.  Such  methods  are 


294:  HISTORY  OF  ASTRONOMY. 

found  in  simultaneous  observations  of  either  Yenus  or 
Mars  from  two  remote  points  of  the  globe.  If  an  as- 
tronomer in  a  high  northern  latitude  observes  the  posi- 
tion of  one  of  these  bodies  when  upon  his  meridian,  and 
another  astronomer  in  a  high  southern  latitude  does 
the  same,  a  comparison  of  these  two  observations  will 
give  the  parallax  of  the  planet,  from  which  we  can 
compute  its  distance  from  the  earth.  The  most  favor- 
able time  for  observing  Mars  is  when  it  is  nearest  the 
earth;  that  is,  at  its  opposition;  and  the  most  favorable 
time  for  observing  Yenus  is  when  it  is  stationary,  or 
near  its  inferior  conjunction.  The  two  places  of  ob- 
servation must  be  in  opposite  hemispheres,  as  remote  as 
possible  from  each  other,  and  it  is  desirable  that  they 
should  both  be  under  the  same  meridian.. 

Lieutenant  Gilliss,  of  the  United  States  Navy,  pro- 
posed an  expedition  to  Chili,  for  the  purpose  of  making 
observations  upon  Dr.  Gerling's  plan  in  connection  with 
the  National  observatory  at  "Washington.  The  Ameri- 
can Philosophical  Society,  and  the  American  Academy 
of  Arts  and  Sciences  commended  this  plan  to  the  favor- 
able action  of  Congress ;  and  in  August,  1848,  Congress 
authorized  the  fitting  out  of  the  expedition,  under  the 
direction  of  the  Secretary  of  the  Navy.  Lieutenant 
Gilliss,  to  whom  the  plan  of  the  expedition  was  mainly 
due,  was  appointed  to  take  charge  of  the  expedition; 
and  passed  midshipman  (now  lieutenant)  Archibald 
MacEea,  and  Henry  C.  Hunter,  were  appointed  as  assist- 
ants. Suitable  wooden  buildings,  to  serve  as  an  ob- 


ASTRONOMICAL  EXPEDITION  TO   CHILI.  295 

servatory  in  Chili,  were  prepared  in  Washington,  and 
shipped  to  Valparaiso  in  the  summer  of  1849. 

The  principal  astronomical  instruments  furnished  for 
the  expedition  were  two  telescopes,  equatorially  mounted, 
a  meridian  circle,  a  clock,  and  three  chronometers. 

The  larger  telescope  was  an  eight  and  a  half  feet 
refractor,  having  an  object-glass  by  Fitz,  of  New  York, 
that  afforded  a  clear  aperture  of  six  inches  and  a  half. 
It  was  fitted  with  clock-work  by  Wm.  Young,  of  Phila- 
delphia, and  by  him  provided  with  a  micrometer  adapted 
both  for  differential  measurements,  and  for  measurements 
of  position  and  distance. 

The  other  telescope  was  a  five  feet  achromatic,  by 
Fraunhofer.  It  was  also  equatorially  mounted,  and  fitted 
with  a  micrometer  by  Young,  of  Philadelphia. 

The  meridian  circle  was  by  Pistor  and  Martins,  of 
Berlin.  The  object-glass  of  the  telescope  had  a  clear 
aperture  of  four  and  one-third  inches,  with  a  focal  length 
of  six  feet.  The  circles  were  thirty-six  inches  in 
diameter,  both  divided  to  2',  and  read  by  two  mi- 
crometer microscopes,  each  to  a  half  second. 

The  series  of  astronomical .  observations,  especially 
contemplated,  consisted  of  differential  measurements 
during  portions  of  the  years  1849,  1850,  1851,  and 
1852,  upon  Venus  and  Mars,  with  stars  conveniently 
situated  in  the  neighborhood  of  their  paths.  The  ob- 
servations of  Venus  chiefly  depended  upon,  were  ob- 
servations near  the  inferior  conjunctions  of  1850  and 
1852.  The  principal  observations  of  Mars  were  near 


296  HISTORY  OP  ASTRONOMY. 

the  times  of  opposition  of  that  planet  in  1849  and  1852. 
To  facilitate  the  observations,  and  to  secure  concert  of 
action,  so  that  observers  in  every  part  of  the  world 
might  use  the  same  stars  of  comparison,  Lieutenant 
Gilliss  prepared  an  ephemeris  of  these  planets  and  suit- 
able stars  of  comparison  during  the  critical  periods. 

The  expedition  set  sail  in  1849,  and  arrived  safely  at 
Valparaiso.  The  observatory  was  located  at  Santiago, 
the  capital  of  Chili,  where  observations  were  commenced 
in  December,  1849.  During  that  season  the  weather 
was  exceedingly  favorable  for  observations.  Of  the  fifty- 
two  pre-appointed  nights  remaining  of  the  first  series 
of  observations  on  Mars,  there  were  only  four  when  no 
observations  could  be  made ;  and  within  these  forty-eight 
nights,  1400  observations  of  the  planet  were  accum- 
ulated. During  the  second  series  on  Mars,  comprising  93 
days,  between  December  16,  1851,  and  March  15,  1852, 
about  2000  differential  measures  were  made  on  seventy- 
eight  nights,  and  meridian  observations  on  eighty  nights. 
Between  October  19,  1850,  and  February  10,  1851,  dif- 
ferential measures  of  the  planet  Yenus  and  comparing 
stars,  were  made  on  fifty-one  nights ;  and  there  were 
seventy-three  meridian  observations,  at  which  time  its 
diameter  also  was  measured.  Owing  to  its  very  fre- 
quent tremulous  motion  in  the  evening  twilight,  the 
differential  measures,  when  approaching  its  eastern 
stationary  terms,  were  often  found  dimcuTt,  and  rarely 
afforded  much  satisfaction.  But  in  the  morning  twi- 
light the  atmosphere  was  tranquil,  and  generally  so  clear 


ASTRONOMICAL  EXPEDITION  TO  CHILI.  297 

that  measures  could  be  continued  long  after  day-light, 
if  the  comparing  star  was  as  bright  as  the  seventh  mag- 
nitude. During  the  second  period  of  Venus  in  1852,  it 
was  possible  to  make  differential  measures  only  on  nine 
evenings  prior  to  the  conjunction,  and  on  eighteen 
mornings  subsequent  to  .it.  There  was  not  a  single 
occasion  when  the  measures  were  wholly  satisfactory. 

As  the  preceding  observations  occupied  only  a  part 
of  the  time  spent  in  Chili,  Lieutenant  Gilliss  devoted  a 
portion  of  the  intermediate  intervals  to  constructing  a 
catalogue  of  stars  between  the  south  pole  and  65°  of 
south  decimation.  Beginning  within  5°  of  the  south 
pole,  a  systematic  sweep  of  the  heavens  was  commenced 
in  zones  or  belts  24'  wide.  "Working  steadily  toward 
the  zenith  on  successive  nights,  until  compelled  to  re- 
turn below  again  to  connect  in  right  ascension,  the  place 
of  every  celestial  body  that  passed  across  the  field  of  the 
telescope,  to  stars  of  the  tenth  magnitude,  was  carefully 
noted  down.  The  space  immediately  surrounding  the 
south  pole  was  swept  in  one  belt  of  5°  by  moving  the 
circle.  Above  the  polar  belt,  forty-eight  other  belts  were 
observed,  making  in  all  24°  12'  of  declination,  within 
which  were  obtained  33,600  observations  of  some  23,000 
stars;  more  than  20,000  of  them  never  previously 
tabulated. 

"While  astronomical  observations  received  the  principal 
attention,  magnetism  and  meteorology  were  not  neglected. 
The  meteorological  instruments  were  observed  tri-hourly 
during  nearly  three  years,  and  one  day  of  each  month 

13* 


298  HISTORY  OF  ASTRONOMY. 

was  devoted  to  hourly  observations.  The  magnetical 
observations  occupied  nearly  four  hours  of  two  and 
sometimes  three  persons  on  three  days  of  each  month, 
when  all  the  elements  necessary  for  determining  the 
direction  and  the  total  force  of  the  earth's  magnetism 
were  carefully  observed. 

A  minute  record  was  preserved  of  all  the  earthquakes 
experienced  during  the  continuance  of  Lieutenant  Gilliss 
in  Chili.  The  number  of  shocks  recorded  was  125  in 
34  months,  being  an  average  of  about  one  each  week. 
A  seismometer  was  erected,  but  it  was  not  sufficiently 
sensitive,  and  generally  made  tLo  record  of  the  agitations 
of  the  earth's  crust. 

Congress  liberally  ordered  the  publication  of  the  re- 
sults of  this  expedition,  directing  that  the  whole  work 
should  be  well  printed  on  good  paper  of  quarto  size,  and 
well  bound.  The  results  will  be  comprised  in  seven 
volumes,  of  which  the  first  two  have  already  been  pub- 
lished. Yol.  I.  contains  a  full  account  of  Chili,  its 
geography,  climate,  earthquakes,  government,  social 
condition,  mineral  and  agricultural  resources,  commerce, 
etc.,  with  a  narrative  of  the  general  progress  of  the 
expedition.  Vol.  II.  contains  Lieutenant  MacKea's  nar- 
rative of  his  magnetical  expedition  across  the  Andes  and 
pampas  of  Buenos  Ayres,  with  an  account  of  the 
minerals  and  mineral  waters  of  Chili,  their  Indian  anti- 
quities, and  a  description  of  various  mammals,  birds, 
reptiles,  fishes,  Crustacea,  and  plants  collected  by  the  ex- 
pedition. Yol.  III.  will  contain  the  differential  observa- 


ASTBONOMICAL  EXPEDITION  TO  CHILI.  299 

tions  made  for  the  parallaxes  of  Mars  and  Venus  at 
Santiago,  Washington,  Cambridge  (Mass.),  and  Cape  of 
Good  Hope,  together  with  a  discussion  of  the  question 
of  parallax  by  Dr.  Gould.  Yol.  IY.  will  contain  the 
meridian  circle  observations  of  planets,  time  and  azimuth 
stars,  stars  of  Lacaille  never  re-observed  by  others,  and 
a  portion  of  the  zone  observations.  Yol.  Y.  will  con- 
tain the  remainder  of  the  zone  observations.  Yol.  VI. 
will  embrace  the  magnetical  and  meteorological  ob- 
servations ;  and  Yol.  VIE.  will  contain  a  catalogue  of 
the  fixed  stars  observed  by  the  expedition,  embracing 
determinations  of  position  of  more  than  20,000  stars 
never  before  tabulated. 


SECTION  III. 

ASTRONOMICAL  RESULTS  OP  PUBLIC  SURVEYS, 

VERY  extensive  surveys  have  been  undertaken,  at  the 
expense  of  the  general  government,  and  some  by  State 
governments,  which  have  indirectly  contributed  very  much 
to  the  science  of  astronomy.  Of  these,  the  survey  of  the 
coast  of  the  United  States  is  the  most  important. 

The  survey  of  the  coast  was  proposed  by  Mr.  Jeffer- 
son, and  was  authorized  by  Congress  in  1807.  Mr. 
Grallatin,  then  Secretary  of  the  Treasury,  sketched  the 
plan  of  a  magnificent  geodetic  work  in  which  the  prin- 
cipal headlands  of  the  coast  should  be  fixed  by  astro- 
nomical observations.  Jn  consequence  of  the  unsettled 
state  of  the  country,  no  active  steps  were  taken  toward 
carrying  this  plan  into  execution  until  1811,  when  Mr. 
Hassler  was  placed  in  charge  of  this  work,  and  was  sent 
to  Europe  to  procure  the  requisite  instruments.  He  did 
not  return  with  the  instruments  until  the  fall  of  1815. 
In  1816  he  commenced  the  survey ;  and  in  1818,  Con- 
gress not  being  satisfied  with  the  progress  of  the  work,  it 
was  stopped. 

In  1832,  the  work  was  revived  by  an  Act  of  Congress, 
and  placed  under  the  direction  of  Mr.  Hassler,  in  whose 


ASTRONOMICAL  RESULTS  OP  PUBLIC  SURVEYS.     301 

hands  it  made  steady  progress  until  his  death  in  1844." 
Professor  A.  D.  Bache  was  then  appointed  to  take  charge 
of  the  survey,  and  has  continued  it  to  the  present  time. 

The  astronomical  part  of  this  survey  consists  in  de- 
termining the  latitude  and  longitude  of  the  stations,  and 
the  direction  of  the  sides  of  the  triangles  with  reference  to 
a  meridian. 

Professor  Bache  has  undertaken  to  determine  the  dif- 
ference of  longitude  between  Greenwich  and  the  most 
important  points  upon  our  coast,  with  the  greatest  pos- 
sible precision.  For  this  purpose  he  has  availed  himself 
of  all  the  astronomical  observations  previously  on  record, 
and  has  instituted  new  observations,  including  those  of 
occultations  and  eclipses,  moon  culminations,  and  the  ex- 
change of  chronometers.  Numerous  observations  have 
been  made  in  Cambridge  and  its  vicinity,  in  the  neighbor- 
hood of  New  York,  Philadelphia,  "Washington,  and 
other  places.  The  difference  of  longitude  between  these 
several  places  has  been  determined  by  means  of  the  elec- 
tric telegraph,  so  that  observations  at  any  of  these  places 
are  equally  available  for  determining  the  longitude  of 
.  each  of  them  from  Greenwich. 

Advantage  has  been  taken  of  the  frequent  passage  of 
steamers  between  Boston  and  Liverpool,  to  make  a 
thorough  comparison  of  the  times  of  those  ports  by 
means  of  chronometers.  For  this  purpose,  as  soon  as  a 
steamer  arrives  in  Boston,  its  chronometers  are  taken  to 
Cambridge  observatory  for  comparison,  where  they  re- 
main until  the  steamer  is  ready  to  return.  Upon  arriving 


302  HISTORY  OF  ASTRONOMY. 

in  Liverpool,  the  chronometers  are  taken  to  the  Liverpool 
observatory,  and  their  errors  determined.  This  method 
of  comparison  has  been  systematically  pursued  since 
1844.  During  the  year  1846,  forty-two  such  compari- 
sons were  made.  In  1848  the  longitude  of  the  Cam- 
bridge observatory  from  Greenwich  was  determined  by 
IMr.  Bond,  from  the  transportation  of  116  chronometers, 
in  thirty -four  voyages  of  the  Cunard  steamers  from  Liver- 
pool to  Boston,  to  be  4h.  44m.  30'5s.  The  longitude 
deduced  from  lunar  occultations  and  solar  eclipses  is 
4h.  44m.  31*9.  During  the  year  1849,  eighty-seven  ad- 
ditional comparisons  were  made,  the  results  of  which 
differ  nearly  two  seconds  of  time  from  those  previously 
obtained  by  astronomical  observations.  The  mean  result 
of  175  chronometers  was  4h.  44m.  30'ls.,  and  it  was  be- 
lieved that  this  result  could  not  be  one  second  in  error. 
The  final  result  of  the  chronometric  expeditions  of  1849, 
1850,  and  1851  was  4h.  44m.  30'66s.  During  the  pro- 
gress of  these  expeditions,  more  than  four  hundred  ex- 
changes of  chronometers  have  been  made. 

The  results  of  the  coast  survey  must  furnish  additional 
materials  for  determining  the  figure  and  dimensions  of 
the  earth.  The  Atlantic  coast  embraces  more  than 
twenty  degrees  of  latitude,  and  its  survey  will  virtually 
furnish  a  measured  arc  of  the  meridian  of  that  extent. 
In  several  places  the  survey  will  furnish  long  continuous 
arcs  upon  the  same  meridian.  Thus  from  Nantucket 
northward  we  shall  obtain  an  arc  of  over  three  degrees ; 
from  Cape  Lookout,  northward  along  the  shore  of  Chesa- 


ASTRONOMICAL  RESULTS  OP  PUBLIC  SURVEYS.      303 

peake  Bay,  we  shall  obtain  an  arc  of  over  five  degrees  * 
and  the  Florida  coast  will  furnish  us  a  continuous  arc  of 
more  than  seven  degrees. 

The  survey  of  the  boundary  between  the  United 
States  and  Texas,  in  the  year  1840,  and  the  survey  of 
the  north-eastern  boundary  of  Maine  between  the  years 
1840  and  1844,  furnished  the  occasion  for  the  determina- 
tion .of  the  latitude  and  longitude  of  numerous  points, 
chiefly  by  Major  J.  D.  Graham  of  the  corps  of  Topo- 
graphical Engineers. 

In  the  summer  of  1835,  Captain  Talcott  was  employed 
by  the  government  of  the  United  States,  to  make  a  series 
of  observations  near  the  southern  line  of  Michigan,  to  settle 
the  disputed  question  of  boundary  between  that  Territory 
and  Ohio.  In  this  expedition  the  latitude  and  longitude 
of  several  places  were  determined  with  great  precision. 

The  most  important  astronomical  survey  hitherto  un- 
dertaken by  any  State  government  was  that  commenced 
by  the  State  of  Massachusetts,  in  1830,  and  completed  in 
1838.  This  survey  was  founded  upon  a  base  of  7*39 
miles  in  length,  measured  on  the  banks  of  the  Connec- 
ticut river,  from  which  a  net-work  of  triangles  com- 
menced and  spread  over  the  entire  State.  The  latitude 
and  longitude  of  twenty-seven  places  were  determined 
independently  by  Mr.  E.  T.  Paine;  and  the  results  of 
the  two  surveys  agree  remarkably  with  each  other. 

A  topographical  survey  of  the  State  of  Maryland  has\ 
recently  been  executed,  under  the  direction  of  Mr.  J.  H. 
Alexander. 


" 

SECTION   IV. 

APPLICATION  OF  THE  ELECTRIC  TELEGRAPH  TO  ASTRO- 
NOMICAL USES. 

IN  1839,  Professor  Morse  suggested  to  M.  Arago,  that 
the  electric  telegraph  would  afford  the  means  of  determin- 
ing the  difference  of  longitude  between  distant  places  with 
an  accuracy  hitherto  unattainable. 

The  first  practical  application  of  this  method  was  made 
by  Captain  Charles  Wilkes,  in  June,  1844,  between 
Washington  and  Baltimore.*  Captain  Wilkes  conducted 
the  experiments  at  "Washington,  and  Lieutenant  Eld  at 
Baltimore.  Two  chronometers,  previously  rated  by  as- 
tronomical observations  in  the  vicinity,  were  brought  to 
the  two  telegraph  offices,  and  were  compared  together 
through  the  medium  of  the  ear,  without  coincidence  of 
beats.  The  comparisons  of  the  chronometers  were  con- 
tinued for  three  days,  and  the  results  indicated  that  the 
Battle  Monument  at  Baltimore  was  1m.  34*87s.  east  of 
the  Capitol.  This  method  will  furnish  differences  of 
longitude  with  a  precision  greater  than  any  method 
hitherto  practiced;  but  it  is  susceptible  of  great  im- 
provements. 

*  Vail's  American  Electro-Magnetic  Telegraph,  page  60. 


APPLICATION  OF  ELECTRIC  TELEGRAPH.  305 

In  the  year  1845,  a  plan  was  adopted  by  Professor  A. 

D.  Bache,  Superintendent  of  the  Coast  Survey,  to  apply 
this  method  in  an  improved  form,  to  the  determination 
of  the  difference  of  longitude  between  the  principal  sta- 
tions of  the  survey ;  and  in  1846  measures  were  taken  to 
connect  in  this  manner  Washington,  Philadelphia,  and 
New  York.     An  arrangement  was  made  with  the  tele- 
graph company,  to  allow  the  use  of  their  line  for  scien- 
tific purposes,  after  the  usual  business   operations  had 
closed  for  the  day.     A  line  of  wires  was  extended  from 
the  General  Post  Office  in  Washington  to  the  Naval  ob- 
servatory ;  a  wire  was  carried  from  the  main  line  through 
the  High  School  observatory  at  Philadelphia ;  and  a  short 
wire  was  carried  from  the  office  in  Jersey  City  to  a  station 
fitted  up  as  a  temporary  observatory,  and  furnished  with 
a  five-feet  transit  telescope  and   an   astronomical  clock. 
The  observations  at  Washington  were  made  by  Professor 

E.  Keith ;  those  at  Philadelphia  by  Professor  E.  O.  Ken- 
dall ;  and  those  at  Jersey  City  by  Professor  E.  Loomis ; 
the  whole  being  under  the  direction  of  Mr.  S.  C.  Walker. 
Each  station  was  furnished  with  a  telegraph  key  and  a 
receiving  magnet. 

Washington,  Philadelphia,  and  Jersey  City  were  thus 
put  in  telegraphic  connection ;  instruments  for  obtaining 
time  were  provided ;  and  to  determine  the  difference  of 
longitude  of  the  stations,  required  simply  the  means  of 
producing  an  instantaneous  effect  observable  at  all  the 
stations.  This  was  to  be  obtained  by  the  motion  of 
the  armatures  of  electro-magnets,  which  had  been  pre- 


306  HISTORY  OF  ASTRONOMY. 

viously  adjusted  by  Mr.  Saxton,  so  as  to  secure  their 
simultaneous  striking  on  the  transmission  of  the  electric 
current.  The  first  trials  which  were  made  for  the  trans- 
mission of  signals  were  unsuccessful.  The  observers 
were  not  provided  with  the  means  of  holding  communi- 
cation by  the  ordinary  mode  of  telegraphing,  and  if  every 
thing  was  not  arranged  exactly  as  had  been  previously 
agreed  upon,  it  was  impossible  to  correspond  for  the  pur- 
pose of  discovering  the  source  of  the  difficulty.  Com- 
munication between  Philadelphia  and  Washington  was 
however  effected  on  the  10th  and  22d  of  October,  and 
the  difference  of  longitude  approximately  obtained.  Sig- 
nals for  time  by  the  clock  were  transmitted,  and  star 
signals  were  exchanged.  On  the  10th  of  October,  the 
transit  of  the  star  2838  Bailey  over  the  seven  wires  of  the 
west  transit  instrument  of  the  "Washington  observatory 
was  signalized  by  Lieutenant  Almy.  The  tune  was  noted 
on  the  Washington  clock  by  Lieutenant  Almy,  and  also 
by  Mr.  Walker,  comparing  together,  by  the  ear,  the  seven 
key  beats  with  the  clock  beats.  The  same  key  beats 
were  also  noted  by  Professor  Kendall  at  Philadelphia. 
These  observations  gave  for  the  difference  of  longitude 
between  the  two  places  7  minutes  and  34  seconds  in 
time. 

The  experience  of  a  few  nights  showed  the  necessity  of 
complete  registering  apparatus,  such  as  is  ordinarily  em- 
ployed by  the  telegraph  companies  ;  and  this  was  accord- 
ingly ordered,  but  was  not  received  in  season  for  use 
during  the  year  1846. 


APPLICATION  OF  ELECTRIC  TELEGRAPH.          307 

In  the  summer  of  1847,  the  experiments  were  renewed 
with  more  complete  apparatus.  After  10  o'clock,  P.M., 
the  three  stations  at  "Washington,  Philadelphia,  and 
Jersey  City,  opposite  New  York,  were  converted  into 
temporary  telegraph  offices,  as  well  as  astronomical  sta- 
tions. The  astronomical  observations  for  clock  correc- 
tions and  personal  equations,  were  arranged  by  Mr.  S.  C. 
Walker,  on  the  model  of  Struve's  celebrated  chronometric 
expedition  between  Pulkova  and  Altona. 

The  following  is  the  method  of  comparing  the  local 
times  at  the  different  stations.  A  signal  is  given  at  the 
first  station  by  pressing  a  key,  as  in  the  usual  mode  of 
telegraphing ;  and  the  observer  at  each  of  the  other  sta- 
tions hears  the  click  caused  by  the  motion  of  the  armature 
of  his  electro-magnet.  The  most  obvious  method  of  com- 
parison consists  in  simply  striking  on  the  signal  key  at 
intervals  of  ten  seconds  ;  the  party  at  the  first  station  re- 
cording the  time  when  the  signals  were  given,  and  the 
party  at  the  second  station  recording  the  time  when  the 
signals  were  received.  After  about  twenty  signals  have 
been  transmitted  from  the  first  station  to  the  second,  a 
similar  set  of  signals  is  returned  from  the  second  station  to 
the  first.  The  objection  to  this  mode  of  comparison  is  that 
it  requires  the  fraction  of  a  second  to  be  estimated  by  the 
ear.  The  party  giving  the  signals  strikes  his  key  in  coin- 
cidence with  the  beats  of  his  clock,  so  that  at  his  station 
there  is  no  fraction  of  a  second  to  be  estimated ;  but  at 
the  other  station,  the  armature  click  will  not  probably  be 
heard  in  coincidence  with  the  beats  of  the  clock,  and  the 


308  :.       HISTORY  OF  ASTRONOMY. 

fraction  of  a  second  is  to  be  estimated  by  the  ear.  Now 
this  fraction  can  not  be  estimated  with  the  accuracy 
which  is  demanded  in  this  kind  of  comparison.  It  is 
found  that  observers  generally  estimate  the  fraction  of  a 
second  too  small  when  using  the  ear  alone,  unassisted  by 
the  eye.  This  error  is  greatest  at  the  middle  date  be- 
tween two  clock  beats,  and  is  found  to  vary  from  0*06  to 
0-18  of  a  second  with  different  observers. 

The  experience  of  a  few  nights  with  the  preceding 
method  of  observation,  suggested  a  second  method  of 
comparison  which  relies  on  the  coincidence  of  a  mean 
solar  and  sidereal  clock  or  chronometer.  A  sidereal 
clock  gains  upon  a  solar  clock  one  second  in  about  six 
minutes ;  and  if  two  such  clocks  are  placed  side  by  side 
they  must  tick  together  once  in  every  six  minutes.  In 
order  to  compare  two  such  clocks,  we  notice  their  move- 
ments, and  wait  until  the  beats  sensibly  coincide,  when 
we  know  that  their  difference  amounts  to  an  entire  num- 
ber of  seconds,  which  is  readily  discovered.  Chronom- 
eters generally  make  two  beats  in  a  second;  so  that 
between  a  clock  which  beats  seconds  of  sidereal  time, 
and  a  chronometer  which  ticks  half  seconds  of  solar 
time,  there  must  be  a  coincidence  every  three  minutes. 

The  following  is  the  method  pursued  in  the  comparisons 
between  Philadelphia  and  Jersey  City.  After  transmit- 
ting a  few  signals  by  the  former  method,  so  as  to  deter- 
mine the  difference  between  the  local  times  of  the  two  sta- 
tions within  a  small  fraction  of  a  second,  the  party  at  the 
first  station  commences  striking  on  his  signal  key  every 


APPLICATION  OF  THE  ELECTBIC  TELEGBAPH.        309 

second,  in  coincidence  with  the  beats  of  his  mean  solar 
chronometer,  and  continues  to  do  so  for  ten  or  fifteen 
minutes  without  interruption.  The  party  at  the  second 
station  compares  the  armature  click  of  his  magnet  with 
the  beats  of  his  sidereal  clock,  and  watches  for  a  coinci- 
dence, and  records  the  time  when  a  coincidence  takes 
place.  When  he  has  obtained  two  or  three  coincidences, 
which  generally  requires  from  ten  to  fifteen  minutes,  he 
breaks  the  electric  circuit,  in  order  to  notify  the  first 
party  to  stop  beating.  He  then  commences  beating 
seconds  by  striking  his  own  signal  key  in  coincidence 
with  the  beats  of  his  sidereal  clock ;  and  the  party  at  the 
first  station  compares  the  armature  clicks  of  his  magnet 
with  the  beats  of  his  solar  chronometer,  and  watches  for  a 
coincidence.  When  he  has  obtained  three  or  four  coin- 
cidences, which  generally  requires  ten  or  twelve  minutes, 
he  breaks  the  electric  circuit,  in  order  to  notify  the 
other  party  to  stop  beating.  The  comparison  of  times  at 
the  two  stations  is  now  complete. 

The  following  is  the  result  of  this  summer's  campaign  : 

DIFFERENCE   OF  LONGITUDE  BETWEEN 


Philadelphia  and 
Washington. 

Philadelphia  and 
Jersey  City. 

Washington  and 
Jersey  City. 

1847,  July 

19, 

7m.  328.969 

4m.  SOs.440 

" 

21, 

33.195 

" 

24, 

33.058 

30.305 

" 

27, 

30.425 

if 

28, 

30.470 

u 

29, 

33.050 

30.407 

12m.    38.552 

Aug. 

3, 

33.134 

30.386 

3.452 

" 

10, 

30.439 

u 

11, 

30.303 

Means.        7m.  333.079  4m.  308.397  12m.    3s. 504 


310  HISTORY  OF  ASTRONOMY. 

For  the  distance  of  250  miles  embraced  in  these  ex- 
periments, the  electric  current  took  no  sensible  time  to 
propagate  itself,  and  it  appeared  that  two  clocks  at  this 
distance  could  be  compared  with  the  same  degree  of 
precision  as  if  they  were  placed  side  by  side. 

During  the  summer  of  1848,  similar  experiments  were 
made  to  determine  the  difference  of  longitude  between 
New  York  and  Cambridge.  A  wire  was  extended  from 
the  Cambridge  observatory,  to  connect  with  the  New 
York  and  Boston  line  near  Brighton ;  and  another  wire 
was  carried  from  the  same  line  to  Mr.  Kutherford's  ob- 
servatory in  the  upper  part  of  New  York  city.  Thus 
the  observatories  at  New  York  and  Cambridge  were 
put  in  telegraphic  communication.  At  New  York  a 
new  forty-five  inch  transit  instrument,  by  Simms,  of 
London,  belonging  to  the  Coast  Survey,  was  used  for 
local  time,  and  a  sidereal  clock  with  chronometers  for 
comparison.  At  Cambridge  a  similar  transit  was  used, 
with  numerous  chronometers  carefully  compared.  The 
observations  at  Cambridge  were  made  by  Professor 
W.  C.  Bond,  and  those  at  New  York  by  Professor 
E.  Loomis.  The  comparisons  of  time  were  made  both 
by  the  method  of  coincidences  already  explained,  and 
by  telegraphing  the  transit  of  the  same  star  over  both 
meridians.  The  latter  method  was  practiced  in  the  fol- 
lowing manner:  c 

A  list  of  zenith  stars  is  selected  beforehand,  and 
furnished  to  each  observer.  When  every  thing  is  pre- 
pared for  observation,  the  Cambridge  astronomer  points 


APPLICATION  OF  THE  ELECTKIC  TELEGKAPH.       311 

his  telescope  upon  one  of  the  selected  stars  as  it  is 
passing  his  meridian,  and  strikes  the  key  of  his  register 
at  the  instant  the  star  appears  to  coincide  with  the  first 
wire  of  his  transit.  He  makes  a  record  of  the  time  by 
his  own  chronometer;  and  the  New  York  astronomer, 
hearing  the  click  of  his  magnet,  records  the  time  by  his 
own  clock.  As  the  star  passes  over  the  second  wire  of 
the  transit  instrument,  the  Cambridge  astronomer  again 
strikes  the  key  of  his  register,  and  the  time  is  recorded 
both  at  Cambridge  and  New  York.  The  same  operation 
is  repeated  for  each  of  the  other  wires.  The  Cambridge 
astronomer  now  points  his  telescope  upon  the  next  star 
of  the  list,  which  culminates  after  an  interval  of  five  01 
six  minutes,  and  telegraphs  its  transit  in  the  same  man- 
ner. In  about  twelve  minutes  from  the  former  observa- 
tion, the  first  star  passes  the  meridian  of  New  York,  when 
the  New  York  astronomer  points  his  transit  instrument 
upon  the  same  star,  and  strikes  the  key  of  his  register 
at  the  instant  the  star  passes  each  wire  of  his  transit. 
The  times  are  recorded  both  at  New  York  and  Cam- 
bridge. The  second  star  is  telegraphed  in  a  similar 
manner.  The  Cambridge  astronomer  now  selects  a 
second  pair  of  stars,  and  repeats  the  same  series  of  opera- 
tions, and  is  followed  by  the  astronomer  at  New  York, 
when  the  star  comes  upon  his  own  meridian.  By  this 
comparison,  the  difference  of  time  between  the  two 
stations  is  obtained  independently  of  the  tabular  places 
of  the  stars. 
On  seven  nights  in  July  and  August  these  methods 


312  HISTORY  OF  ASTRONOMY. 

were  practiced,  during  which  time  12,000  signals  were 
exchanged  between  the  observatories  at  New  York  and 
Cambridge. 

The  personal  equations  for  the  clock  corrections  of  the 
different  observers  were  obtained  by  a  very  extensive 
series  of  comparisons,  894  in  number,  the  transit  of  the 
same  star  over  alternate  wires  of  the  telescope  being 
noted  by  different  observers. 

The  result  of  all  the  comparisons  gave  the  difference 
of  longitude  between  Cambridge  and  Mr.  Kutherford's 
observatory,  11  minutes  and  26.07  seconds. 

During  the  month  of  October,  1848,  the  difference  of 
longitude  between  the  Cincinnati  observatory  and  the 
High  School  observatory  in  Philadelphia  was  also  de- 
termined by  telegraph  for  the  use  of  the  United  States 
Coast  Survey.  A  wire  was  carried  from  the  Cincinnati 
observatory  to  the  Philadelphia  line,  thus  putting  the 
observatories  of  Philadelphia  and  Cincinnati  in  tele- 
graphic communication.  The  series  of  observations  here 
made  was  substantially  the  same  as  had  been  practiced 
two  months  before  between  New  York  and  Cambridge. 
A  sidereal  clock  in  Philadelphia  was  compared  with  a 
solar  chronometer  in  Cincinnati,  by  beating  seconds  upon 
the  key  of  the  telegraph  register  for  fifteen  minutes,  and 
noting  the  instants  of  coincident  beats.  Transits  of  the 
same  stars  over  both  meridians  were  also  telegraphed, 
as  had  been  practiced  between  Cambridge  and  New 
York.  These  comparisons  were  made  on  six  differ- 
ent nights,  and  gave  the  difference  of  longitude  be- 

' 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       313 

tween   Philadelphia  and   Cincinnati   37   minutes  20.48 
seconds.  •  . 

In  the  course  of  the  comparisons  for  longitude  by  tele- 
graph, up  to  the  autumn  of  1848,  many  thousand  signals 
were  transmitted,  and  all  by  the  hands  of  a  human 
operator.  But  it  is  impossible  for  human  fingers  to 
move  with  the  precision  of  machinery;  and,  after  the 
first  successful  trial  of  the  telegraph  for  longitude,  it 
became  evident  that  an  important  advantage  would  be 
secured  if  the  clock  could  be  made  to  transmit  its  own 
signals.  The  desideratum  was  to  make  an  astronomical 
clock  break  the  electric  circuit  every  second,  so  that  prac- 
tically it  might  be  said  that  its  beats  could  be  heard  along 
the  entire  line  of  telegraph  communication ;  and  this 
must  be  done  in  such  a  manner  as  not  to  affect  the  rate 
of  the  clock.  A  number  of  different  methods  of  ac- 
complishing this  object  were  speedily  proposed ;  but  as 
several  contrivances  of  a  similar  kind  had  previously 
existed,  it  is  thought  best  to  notice  them  all  in  chrono- 
logical order. 

THE  ELECTRIC  CIRCUIT  BROKEN  BY  A  CLOCK. 

The  first  invention  for  breaking  the  electric  current  by 
clock-work  appears  to  be  due  to  Professor  Steinheil,  of 
Munich,  who  previous  to  September,  1839,  had  perfected 
a  method  for  causing  any  number  of  clocks  to  indicate 
exactly  the  same  time.*  This  was  accomplished  by 
means  of  an  arrangement  which  enabled  the  regulating 

*  Moigno'a  Traite  de  Telegraphie  Electrique,  page  337. 
14 


314  HISTORY  OF  ASTRONOMY. 

clock,  at  the  end  of  every  hour,  to  advance  or  put  back 
the  hands  of  the  subordinate  clocks,  so  that  all  should 
indicate  exactly  .the  same  time.  This  contrivance  was  as 
follows :  One  of  the  wheels  in  each  clock  carries  a  flat 
piece  in  the  form  of  a  spiral,  which  during  the  hour, 
slowly  raises  a  weight  acting  on  a  lever.  The  weight, 
when  raised,  is  sustained  like  the  trigger  of  a  musket, 
and  the  spiral  piece  has  a  notch  in  which  the  lever  may 
be  caught.  When  the  instant  arrives  for  the  standard 
clock  to  regulate  all  the  others,  an  electro-magnet  (ren- 
dered magnetic  by  the  instantaneous  passage  of  an  electric 
current)  attracts  its  armature,  causing  the  arm  of  the  lever 
to  fall,  and  in  its  fall  it  catches  in  the  notch  of  the  spiral 
piece,  with  which  the  hands  of  the  clock  are  connected. 
If  during  the  preceding  hour,  the  clock  has  gained  or  lost 
time,  the  fall  of  the  lever  carries  backward  or  forward 
the  spiral  piece,  and  with  it  the  hands  of  the  clock,  so 
that  on  every  dial  the  hands  indicate  exactly  the  same 
time.  Thus  all  the  clocks  of  a  large  city  may  be  made 
to  strike  the  hour  at  the  same  instant. 

For  the  ordinary  purposes  of  business,  it  is  not  neces- 
sary that  the  agreement  of  the  clocks  should  extend  to 
very  minute  fractions  of  time ;  if  this  was  however  de- 
sired, the  standard  clock  might  act  directly  upon  the 
pendulums  of  the  subordinate  clocks,  so  as  to  render  their 
times  of  vibration  perfectly  equal. 

In  the  year  1840,  Professor  Wheatstone,  of  London, 
invented  an  apparatus,  called  an  electro-magnetic  clock, 
for  enabling  a  single  clock  to  indicate  exactly  the  same 


APPLICATION   OF  THE  ELECTRIC  TELEGRAPH.       315 

time  in  as  many  different  places  as  may  be  required.* 
In  the  electro-magnetic  clock,  all  the  parts  employed  in 
an  ordinary  clock  for  maintaining  and  regulating  the 
power  are  entirely  dispensed  with.  It  consists  simply  of 
a  face  with  its  second,  minute,  and  hour  hands,  and  of  a 
train  of  wheels  which  communicate  motion  from  the 
arbor  of  the  second's  hand  to  that  of  the  hour  hand,  in 
the  same  manner  as  in  an  ordinary  clock  train.  A  small 
electro-magnet  is  caused  to  act  upon  a  peculiarly  con- 
structed wheel,  placed  on  the  second's  arbor,  in  such  a 
manner  that  whenever  the  temporary  magnetism  is  either 
produced  or  destroyed,  the  wheel,  and  consequently  the 
second's  hand,  advances  a  sixtieth  part  of  its  revolution. 
It  is  obvious  then  that  if  an  electric  current  can  be  alter- 
nately established  and  arrested,  each  resumption  and 
cessation  lasting  for  a  second,  the  instrument  now  de- 
scribed, although  unprovided  with  any  internal  maintain- 
ing or  regulating  power,  would  perform  all  the  usual 
functions  of  a  perfect  clock.  The  manner  in  which  this 
apparatus  is  applied  to  the  clocks,  so  that  the  movements 
of  the  hands  of  both  may  be  perfectly  simultaneous  is  the 
following : 

On  the  axis  which  carries  the  scapement  wheel  of  the 
primary  clock,  is  fixed  a  small  disc  of  brass,  which  is 
first  divided  on  its  circumference  into  sixty  equal  parts ; 
each  alternate  division  is  then  cut  out  and  filled  with  a 
piece  of  wood,  so  that  the  circumference  consists  of 
thirty  ^regular  alternations  of  wood  and  metal.  An  ex- 

*  Abstracts  of  the  Philosophical  Transactions  vol  iv.,  page  249. 


316  HISTORY  OF  ASTRONOMY. 

tremely  light  brass  spring,  which  is  secured  to  a  block  of 
ivory  or  hard  wood,  and  which  has  no  connection  with 
the  metallic  parts  of  the  clock,  rests  by  its  free  end  on 
the  circumference  of  the  disc.  A  copper  wire  is  fastened 
to  the  fixed  end  of  the  spring,  and  proceeds  to  one  end 
of  the  wire  of  the  electro-magnet ;  while  another  wire 
attached  to  the  clock-frame  is  continued  until  it  joins  the 
other  end  of  that  of  the  same  electro-magnet.  A  con- 
stant voltaic  battery,  consisting  of  a  few  elements  of  very 
small  dimensions,  is  interposed  in  any  part  of  the  circuit. 
By  this  arrangement,  the  circuit  is  periodically  made  and 
broken,  in  consequence  of  the  spring  resting  for  tme 
second  on  a  metal  division,  and  the  next  second  on  a 
wooden  division.  The  circuit  may  be  extended  to  any 
length  ;  and  any  number  of  electro-magnetic  instruments 
may  be  thus  brought  into  sympathetic  action  with  the 
standard  clock. 

In  the  year  1840,  Mr.  Alexander  Bain,  of  London,  in- 
vented an  arrangement  by  which  it  was  proposed  to  work 
a  great  number  of  clocks  simultaneously.*  The  follow- 
ing is  the  method  by  which  the  regulating  clock  was 
made  to  break  the  electric  circuit.  A  B  is  a  pendulum 
vibrating  seconds.  C  is  a  plate  of  ivory  affixed  to  the 
frame  of  the  clock,  in  the  middle  of  which  is  inserted 
a  slip  of  brass  D,  communicating  with  the  positive  pole 
of  a  voltaic  battery.  To  the  pendulum  is  attached  a  very 
light  brass  spring  E  in  such  a  manner  that  every  vibra- 

*  Applications  of  the  Electric  Fluid  to  the  Useful  Arts,  *by  Mr. 
Alexander  Bain,  page  9f. 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       317 


tion  of  the  pendulum  brings  the  free  end  of  the  spring 

into  contact  with  the  strip  of  brass  D,  thus  completing 

the    electric    circuit    through    the 

upper  part  of  the  pendulum  to  the 

negative  pole  of  the  battery ;  while 

the  circuit  is  broken  as  soon  as  the 

spring  touches  the  ivory. 

Subsequently  Mr.  Bain  adopted 
the  arrangement  of  closing  and 
breaking  the  circuit  by  means  of  a 
short  brass  bar,  placed  in  a  horiz- 
ontal position  near  the  middle  of 
the  pendulum;  the  bar  being  slid 
back  and  forth  about  one  inch  at 
each  vibration  of  the  pendulum. 

In  1844,  Mr.  Joseph  Saxton 
proposed  to  break  the  electric 
circuit  by  a  pin  on  the  pendulum  rod  striking  a  small 
tilt  hammer,  and  also  making  the  circuit  by  a  lancet- 
shaped  point  of  platinum  at  the  bottom  of  the  rod 
passing  through  a  globule  of  mercury.  Early  in  1846, 
he  proposed  both  methods  again,  when  objections  were 
made  against  them  on  the  supposition  that  the  current  of 
electricity  passing  through  the  pendulum  rod  might  affect 
the  rate  of  the  clock.  To  meet  this  objection,  he  pro- 
posed to  insulate  the  pin  by  a  piece  of  ivory,  or  use  a 
glass  pin.  Or  if  the  other  method  was  used,  instead  of 
passing  the  current  through  the  rod,  he  proposed  to  at- 
tach at  the  top  of  the  rod  a  small  lever  to  be  raised  by 


318  HISTORY  OF  ASTRONOMY. 

the  motion  of  the  pendulum;  the  lever  to  turn  on  a 
center  near  the  point  of  suspension,  but  insulated 
from  it. 

In  1849,  the  arrangement  with  a  glass  pin  moving  a 
platinum  tOt-hammer  was  applied  by  Mr.  Saxton  to  the 
Hardy  clock  of  the  Coast  Survey,  and  put  in  operation  at 
the  Seaton  station  in  July  of  that  year.  This  arrange- 
ment is  shown  in  the  annexed  cut.  ABC  represents  a 


fine  platinum  wire,  mounted  on  a  pivot  at  B,  the  end  A 
being  somewhat  heavier  than  the  other,  and  resting  upon 
a  metalic  bed  D.  At  C  the  wire  is  bent  so  as  to  form  an 
obtuse  angle.  The  wire  E  goes  from  D  to  one  pole  of 
the  battery,  while  the  wire  H  from  the  other  pole  of  the 
battery,  communicates  with  the  metallic  support  Gr,  and 
thence  with  the  wire  A  B.  When  the  -end  A  of  the 
platinum  wire  rests  upon  the  support  D,  it  is  evident  that 
the  electric  circuit  is  complete.  This  apparatus  is  placed 
near  the  middle  of  the  pendulum  (a  portion  of  which, 
I  K,  is  represented  in  the  cut),  and  just  in  front  of  it,  so 
that  the  pendulum  may  swing  behind  it  without  obstruc- 
tion. A  small  glass  pin  F,  about  half  an  inch  in  length, 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.         319 


is  attached  to  the  pendulum  in  such  a  position  that,  at 
every  vibration  of  the  pendulum,  the  pin  slightly  im- 
pinges upon  .the  angle  C,  of  the  platinum  wire  and  forces 
up  the  end  A.  As  soon  as  the  pin  has  passed  the  point 
C,  the  end  A  falls  back  again  upon  its  support  D.  Thus 
at  every  vibration  of  the  pendulum,  the  end  of  the  plati- 
num wire  is  lifted  about  a  tenth  of  a  second,  and  rests 
upon  D  during  the  remaining  nine  tenths  of  the  second ; 
that  is,  the  electric  circuit  is  closed  about  nine  tenths  of 
every  second,  and  is  open  during  the  remaining  tenth. 

The  method  first  proposed  by  Mr.  Saxton  in  1844,  is 
the  one  which  has  been  employed  at  the  "Washington 
observatory  since  1849.  A  small  piece  of  metal  M  is 
attached  to  the  back  of  the  clock,  near 
the  lower  extremity  of  the  pendulum, 
and  upon  it  is  placed  a  small  globule  of 
mercury,  so  that  the  index  B  attached  to 
the  lower  extremity  of  the  pendulum  may 
pass  through  the  globule  of  mercury  once 
in  every  vibration.  A  wire  from  one 
pole  of  the  battery  is  connected  with  the 
supports  of  the  pendulum  C,  and  a  second 
wire  from  the  other  pole  of  the  battery 
connects  with  the  metallic  support  of  the 
mercury  globule.  If  now  the  pendulum 
were  at  rest,  with  the  point  B  in  the 
mercury,  it  is  evident  that  the  electric 
circuit  would  be  complete  through  the 
pendulum.  If  then  the  pendulum  be  set  in  motion,  it 


320  HISTOEY  OF  ASTRONOMY. 

will  break  the  circuit  whenever  it  passes  out  of  the 
mercury,  and  restore  it  again  as  soon  as  it  touches  the 
mercury. 

In  1843,  at  the  launch  of  the  frigate  Earitan  at 
Philadelphia,  an  attempt  was  made  to  ascertain  the  rate 
of  motion  of  the  ship  when  running  off  the  ways,  by 
observing  the  time  required  for  certain  marks  on  the 
side  of  the  ship  to  pass  fixed  points  of  sight.  As  this 
method  proved  unsatisfactory,  Mr.  Saxton  contrived  a 
machine  for  registering  the  motion  with  certainty.  This 
contrivance  consisted  of  a  half  second's  pendulum,  with 
a  pin  projecting  from  the  rod.  This  pin  acted  on  an 
angle  piece  attached  to  a  lever  which  had  a  small  conical 
cup  at  the  end,  containing  a  mixture  of  oil  and  ver- 
milion. The  cup  had  a  small  hole  at  its  apex,  and  the 
mixture  was  prevented  from  flowing  out  by  the  capillary 
action  of  a  small  lock  of  cotton.  A  reel,  containing 
about  60  feet  of  white  cotton  tape,  was  so  placed  that 
the  tape  passed  under  the  cup  as  it  was  drawn  out,  and 
had  a  red  dot  struck  on  it  every  half  second  by  the 
vibration  of  the  pendulum. 

Some  time  afterward,  when  the  steam  frigate  Princeton 
was  ready  to  be  launched,  Mr.  Saxton  constructed  a 
machine  of  the  kind  here  described.  A  wire  about  two 
feet  long  was  attached  to  a  small  ring  that  hooked  on  a 
detent,  which  held  the  pendulum  when  it  was  raised  up 
on  one  side.  The  other  end  of  the  wire  was  attached 
to  the  bow  of  the  ship,  so  that"  the  first  motion  of  the 
ship  would  unhook  the  pendulum,  which,  falling  to  its 


APPLICATION  OF  THE  ELECTKIC  TELEGRAPH.        321 

lowest  point,  caused  the  lever  to  strike  a  dot  on  the  tape 
at  the  first  quarter  second,  and  afterwards  at  each,  half 
second  to  the  end  of  the  tape.  This  pendulum  had  no 
maintaining  power,  except  its  own  gravity,  as  it  was  only 
required  to  act  for  a  few  seconds.  Electricity  was  not 
used  in  this  experiment ;  but  this  machine  was  the  germ 
of  the  contrivances  described  on  page  318  for  breaking 
the  electric  circuit. 

In  the  year  1847,  Mr.  J.  J.  Speed,  of  Detroit,  Michigan, 
conceived  a  plan  for  causing  all  the  clocks  of  a  large  city 
to  indicate  the  same  time.  He  proposed  to  have  all  the 
clocks  in  the  city  connected  with  galvanic  circuits,  and 
operated  from  soi^e  central  battery,  the  hands  on  the 
clocks  moving  only  at  given  intervals,  and  at  the  instant 
the  circuit  should  be  closed.  To  close  and  break  the 
circuit,  he  had  a  clock  constructed  with  a  tilt-hammer, 
which  was  lifted  by  a  projecting  tooth  on  one  of  the 
wheels  of  the  clock.  The  credit  of  this  part  of  the  in- 
vention is  conceded,  however,  to  Mr.  C.  F.  Johnson,  of 
Owego,  N.  Y.,  and  was  patented  by  him  in  1846.  The 
idea  of  applying  the  galvanic  circuit  to  give  motion  to 
house  clocks  by  means  of  the  tilt  hammer,  is  claimed  by 
Mr.  Speed.  Has  attention  being  soon  afterward  directed 
to  other  objects,  Mr.  Speed  never  carried  his  plan  irto 
execution,  and  the  clock  which  he  ordered  to  be  con- 
structed with  the  tilt-hammer  arrangement  is  now  the 
property  of  the  United  States  Coast  Survey. 

Dr.  Locke,  of  Cincinnati,  in  the  autumn  of  1848,  in- 
vented an  arrangement  for  breaking  the  electric  circuit 

14* 


322 


HISTOKY  OF  ASTRONOMY. 


by  means  of  a  tilt-hammer.  Dr.  Locke  employs  a  wheel 
with  sixty  teeth  attached  to  the  axis  of  the  escapement 
wheel.  Bach  tooth  in  succession  strikes  against  the 
handle  of  a  platinum  tilt-hammer,  A  C,  weighing  about 
two  grains,  and  knocks  up  the  hammer,  which  almost 
immediately  falls  to  a  state  of  rest  on  a  bed  of  platinum. 


The  fulcrum  B  of  the  tilt-hammer  and  the  platinum 
bed  rest  severally  on  a  small  block  of  wood.  Each  is 
connected  "by  wires  D  and  E  with  a  pole  of  the  galvanic 
battery,  and  the  circuit  is  alternately  broken  and  com- 
pleted by  the  rising  and  falling  of  the  hammer.  The 
circuit  is  open  about  the  one  tenth  of  a  second,  and 
closed  the  remaining  nine  tenths  of  each  second.  This 
arrangement  was  first  tested  on  the  17th  of  November, 
1848,  on  the  Cincinnati  and  Pittsburg  line,  about  four 
hundred  miles  in  length.  The  circuit  was  broken  every 
second  by  the  motion  of  the  clock;  and  the  fillet  of 
paper  being  allowed  to  run  off  from  the  reel  of  the  tele- 
graph register,  it  was  graduated  into  equal  portions, 


APPLICATION  OP  THE  ELECTKIC  TELEGRAPH.        323 

consisting  of  an  indented  line  about  nine  tenths  of  an 
inch  in  length,  followed  by  a  blank  space  of  about  one 
tenth  of  an-  inch. 

The  Congress  of  the  United  States  have  expressed 
their  conviction  of  the  importance  of  this  invention,  by 
awarding  the  sum  of  ten  thousand  dollars  to  Dr.  Locke 
for  his  invention,  and  directing  that  a  clock  upon  this 
principle  should  be  constructed  for  the  use  of  the  ob- 
servatory at  Washington.  This  clock  was  completed  in 
1850,  and  has  been  set  up  for  use  at  the  observatory. 

In  1849  Professor  O.  M.  Mitchell,  of  Cincinnati,  in- 
vented a  method  of  breaking  the  electric  circuit  by  means 
of  a  delicate  .fibre  attached  to  the  pendulum  which  acts 
upon  a  cruciform  lever,  and  thus,  in  every  vibration  of 
the  pendulum,  allows  a  metallic  point  to  dip  into  a  cup 
of  mercury,  which  completes  the  circuit  In  the  annexed 
figure,  A  B  represents  the  lower  extremity  of  the  pen- 


dulum;   B  C  is  a  delicate  fibre,   one  end  of  which  is 
attached  to  the  pendulum,  and  the  other  to  one  arm  of 


324  HISTORY  OF  ASTRONOMY. 

a  cross,  C  E  F  Gr,  formed  of  platinum  wire,  mounted  like 
a  wheel  upon  the  axis  D.  The  arm  D  G  of  the  cross 
being  slightly  the  heaviest,  rests  upon  one  end  of 
a  glass  tube,  Gr  H,  bent  in  the  form  of  a  syphon,  and 
containing  mercury,  while  the  other  end,  H,  of  the  tube 
is  without  the  clock  case,  so  that  it  can  be  reached 
without  opening  the  case.  The  axis  D  of  the  cross 
communicates  by  a  wire  with  one  pole  of  the  battery, 
while  the  .end  H  of  the  mercury  tube  communicates  with 
the  other  pole.  As  the  pendulum  approaches  to  the 
extreme  left  of  its  arc  of  vibration,  it  pulls,  by  means 
of  the  fibre  B  C,  upon  the  arm  C  D,  and  lifts  the  end  Gr 
out  of  the  mercury,  thus  breaking  the  electric  circuit ; 
but  during  the  remaining  part  of  each  double  vibration, 
the  point  Gr  rests  upon  the  mercury,  and  the  electric 
circuit  is  complete.  Accordingly,  in  Professor  Mitchell's 
register,  the  clock  dots  are  made  at  intervals  of  two 
seconds. 

In  October,  1848,  Professor  W.  C.  Bond  made  the 
drawings  for  a  clock  to  break  the  electric  circuit,  and 
his  clock  was  completed  in  1850.  In  this  clock  the 
axis  of  the  escapement  wheel,  and  also  the  axis  of  the 
steel  pallets  are  insulated  by  a  ring  of  shellac.  Wires 
from  the  two  poles  of  the  battery  are  connected  with 
each  axis,  so  that  when  either  pallet  comes  in  contact 
with  an  escapement  tooth,  the  electric  circuit  is  closed ; 
and  when  the  contact  is  broken  (as  it  must  be  at 
every  oscillation  of  the  pendulum)  the  electric  circuit 
is  opened. 


APPLICATION  OF   THE  ELECTRIC  TELEGRAPH.       325 


MODE  OF  REGISTERING  THE  OBSERVATIONS. 

The  most  obvious  mode  of  registering  the  beats  of  the 
clock  is  upon  a  long  fillet  of  paper,  after  the  ordinary 
method  of  telegraphic  communications.  If  the  paper  be 
allowed  to  run  through  an  ordinary  Morse  registering  ap- 
paratus, and  the  circuit  be  broken  every  second  by  the 
clock,  the  graver  will  trace  upon  the  "paper  a  series  of 
lines  of  equal  length  separated  by  short  interruptions 
thus: 


It  is  easy  to  reverse  the  action  of  the  graver,  so  that 
when  the  circuit  is  complete,  the  paper  shaU  be  entirely 
free,  and  a  dot  be  made  by  the  breaking  of  the  circuit.  A 
paper  graduated  into  seconds  by  this  arrangement  ex- 
hibits dots  with  long  intervening  spaces  thus : 


instead  of  long  lines  with  short  blanks,  as  shown  be- 
fore. 

In  order  to  indicate  the  commencement  of  the  minute, 
a  dot  may  be  omitted  at  the  end  of  every  60  seconds. 
This  is  accomplished  in  Dr.  Locke's  clock  by  omitting 
one  tooth  in  the  wheel  which  breaks  the  circuit,  as  shown 
at  H  in  the  figure  page  322. 

The  mode  of  using  the  register  for  marking  the  date  of 
any  event,  is  to  tap  on  a  break-circuit  key,  simulta- 


326 


HISTOEY  OF  ASTRONOMY. 


neously  with  the  event.  The  beginning  of  the  short  line 
thus  printed  upon  the  graduated  scale  of  the  register, 
fixes,  by  a  permanent  record,  the  date  of  the  event. 
Thus  A  represents  such  a  record  printed  upon  the  gradu- 
ated paper : 

A 


By  tapping  upon  the  key  at  the  instant  a  star  is  seen 
to  pass  each  of  the  wires  of  a  transit  instrument,  the  ob- 
servation is  instantly  and  permanently  recorded.  The 
usual  rate  of  progress  of  the  fillet  under  the  pen  is  about 
one  inch  per  second,  and  the  observations  are  read  off  by 
means  of  a  graduated  transparent  scale,  about  an  inch 
square,  as  represented  in  the  annexed  cut,  consisting  of 
equidistant  and  parallel  lines,  ruled 
upon  a  piece  of  glass,  by  means  of 
a  diamond  or  etched  with  fluoric 
acid.  .  If  the  interval  between  the 
second  dots  be  greater  than  the 
breadth  of  the  scale,  the  scale  is 
turned  obliquely  across  the  fillet, 
until  the  first  and  last  divisions  exactly  comprehend  the 
space  between  the  two  second  dots.  Let  the  distance 
from  4s.  to  5s.  on  the  above  scale,  be  the  distance  on  the 
fillet  between  the  fourth  and  fifth  seconds,  and  let  the  dot 
a  between  them  represent  the  observation.  It  appears, 
by  inspection,  that  the  observation  was  recorded  between 
4-7  and  4'8  seconds.  The  distance  of  a  from  the  nearest 
scale  division  may  be  estimated  to  tenths.  Thus  time  is 


APPLICATION  OP  THE  ELECTKIC  TELEGRAPH.       327 


accurately  measured  to  tenths,  and-  may  be  estimated  to 
hundredths  of  a  second.  On  some  ac- 
counts it  is  more  convenient  to  employ 
a  scale  consisting  of  diverging  lines,  as 
represented  in  the  annexed  cut,  so  that 
the  breadth  of  the  scale  may  always 
exactly  comprehend  the  interval  be- 
tween the  second  dots,  which  intervals 
must  necessarily  vary  somewhat  in  length. 

It  is  important  that  the  paper  upon  which  the  observa- 
tions are  recorded  should  be  reduced  to  a  convenient 
form  for  preservation.  The  long  fillet  of  paper  employed 
in  ordinary  telegraphing,  is  very  inconvenient  for  astro- 
nomical purposes. .  If  the  paper  is  allowed  to  run  off  at 
the  rate  of  one  inch  per  second,  the  length  of  fillet  re- 
quired for  one  hour's  observations  would  be  3600  inches,  or 
300  feet;  and  for  a  single  night's  work  of  an  observatory, 
a  length  of  nearly  half  a  mile  would  be  required.  The 
inconvenience  of  managing  such  a  strjp  of  paper  detracts 
materially  from  the  value  of  the  method. 

In  the  summer  of  1849,  Mr.  Saxton  completed  a  re- 
gister which  is  well  adapted  to  the  regular  work  of  an 
observatory.  It  consists  of  a  cylinder  which  may  be 
made  of  any  convenient  dimensions,  say  six  inches  in 
diameter  and  two  feet  long,  enveloped  with  paper  which 
may  be  removed  at  pleasure.  This  cylinder  is  made  to 
revolve  with  a  uniform  motion,  while  the  registering  pen 
moves  forward  at  the  rate  of  one  tenth  of  an  inch  to 
every  revolution  of  the  cylinder.  Thus  the  pen  is  made 


328 


HISTORY  OF  ASTKONOMY. 


I 


to  trace  a  spiral  on  the  cylinder,  and  one  sheet  of  paper, 
twelve  inches  by  twenty,  lasts  for  more  than  two  hours 
of  constant  work.  Two  sheets  will  contain 
an  ordinary  night's  work. 

In  order  to  secure  the  full  advantage  of 
this  method,  it  is  important  that  the  paper 
which  contains  the  register  be  made  to  ad- 

,s  vance  with  entire  uniformity.  The  Messrs. 
Bond  have  invented  for  this  purpose  a 

^  machine  which  they  call  the  Spring  Gov- 
ernor, consisting  of  a  train  of  clock-work 

^    connected  with  the  axis  of  a .  fly-wheel.     It 

H  has  an  escapement-wheel,  into  the  teeth  of 
which  pallets  are  operated  by  the  oscillations 

5>  of  a  pendulum,  as  in  ordinary  clocks,  the 
wheel  being  so  connected  with  its  axis  by 
a  spring  as  to  allow  the  axis  to  move  while 

^  the  wheel  is  detained  by  the  pallets.  The 
register  is  made  upon  a  sheet  of  paper 

*>   wrapped  round  a  cylinder.      The   annexed 

%  specimen  is  a  fac-simile,  taken  from  a  record 
sheet  used  at  the  Cambridge  observatory. 

^  A  B  shows  the  signal  announcing  the  ap- 
proach of  a  star  to  the  right  ascension  wires 

*    of  the  transit   instrument;    C  indicates  the 

„  passage  of  the  star  over  the  first  wire ;  and 
D-indicates  the  passage  over  the  second  wire 

o  The  passage  over  the  first  wire  took 
place  at  7h.  16m.  7s.4,  and  the  passage 
over  the  second  wire  at  7h.  16m.  11s.  4. 


APPLICATION   OP  THE   ELECTRIC  TELEGRAPH.       329 

Mr.  Kerrison  has  invented  a  method  of  regulating  the 
motion  of  the  registering  cylinders  by  means  of  two 
short  pendulums  attached  to  cranks,  in  such  a  manner,- 
that  the  one  crank  shall  be  at  its  maximum  effect  when 
the  other  is  passing  its  dead  point.  The  weight,  by 
which  the  works  are  kept  in  motion,  has  in  this  arrange- 
ment a  considerable  influence  on  the  velocity ;  conse- 
quently it  was  found  very  difficult  to  regulate  it,  and 
when  regulated,  almost  impossible  to  keep  it  so.  The 
number  of  pendulums  were  increased  by  Mr.  Kerrison  in 
the  hope  of  overcoming  the  difficulty,  but  hitherto 
without  success. 

Professor  Mitchell's  method  of  recording  right  ascen- 
sions was  invented  in  1849,  and  consists  of  a  horizontal 
disc  which  is  made  to  revolve  with  uniform  velocity  once 
a  minute  on  a  vertical  axis.  This  disc  carries  either  a 
metal  plate,  or  a  paper  disc,  on  which  the  time  and  ob- 
servations are  recorded  by  pens  drawn  by  electro-mag- 
nets. At  every  alternate  second,  a  dot  is  struck  by  the 
time-pen  on  the  paper.  When  the  disc  has  performed 
one  revolution,  a  tooth  upon  the  axis  of  the  disc  takes 
hold  of  a  fixed  rack,  and  moves  the  traveling  frame, 
which  carries  the  center  of  the  disc  through  the  tenth 
of  an  inch,  when  a  new  circumference  of  time  dots  is 
commenced.  The  observation  dots  fall  intermediate 
between  the  minute  circles  and  second  dots,  and  are  struck 
so  as  to  distinguish  them  by  form  from  the  time  dots. 


330  HISTORY   OF  ASTRONOMY. 

.     OBSERVATIONS    FOR    LONGITUDE    SINCE    THE    AUTUMN 

OF    1848. 

On  the  17th  of  November,  1848,  Professor  Locke,  at 
Cincinnati,  undertook  so  to  connect  his  clock  with  the 
telegraph  line  that 'its  beats  should  be  heard  and  regis- 
tered at  Pittsburg,  a  distance  of  about  four  hundred 
miles.  The  circuit  was  broken  every  second  at  Cin- 
cinnati by  the  motion  of  the  clock ;  and  at  Pittsburg, 
the  fillet  of  paper  being  allowed  to  run  off  from  the  reel 
of  the  telegraph  register,  it  was  graduated  into  equal 
portions,  consisting  of  an  indented  line  about  nine-tenths 
of  an  inch  in  length,  followed  by  a  blank  space  of  about 
one-tenth  of  an  inch.  The  two  correspond  to  one  second 
of  time,  commencing  with  the  beginning  of  the  line. 
This  experiment  was  continued  for  two  hours,  during 
which  time  the  seconds  of  the  Cincinnati  clock  were 
registered  on  the  running  fillet  of  paper  at  all  the  offices 
along  the  line.  In  order  to  distinguish  the  hours  and 
minutes  upon  this  graduated  paper,  Dr.  Locke  proposed 
to  make  the  beginning  of  the  ordinary  minutes  omit 
one  blank  space  ;  the  beginning  of  five  minutes  omit  two, 
of  ten  minutes  three,  and  of  •  an  hour  omit  four  con- 
secutive blank  spaces.  Thus,  ordinary  beginnings  of 
minutes  have  continuous  lines  of  two  seconds,  fives  three, 
tens  four,  and  hours  Jive  seconds. 

*,  In  the  month  'of  January,  1849,  a  clock  upon  Dr. 
Locke's  construction  was  employed  for  printing  transits 
of  stars  over  different  meridians  for  the  determination 


APPLICATION  OP  THE  ELECTRIC  TELEGRAPH.       331 

of  longitude.  The  observatories  at  Cambridge,  New 
York  and  Philadelphia,  were  all  put  in  communication 
with  each  other,  and  with  "Washington  city.  The  clock 
which  was  to  be  employed  was  set  up  in  Philadelphia, 
and  connected  with  the  telegraph  line.  Simultaneously 
with  the  beats  of  this  clock,  a  click  was  heard  of  the 
magnets  at  Cambridge,  New  York  and  Washington. 
The  paper  being  allowed  to  run  off  from  the  reel,  it  was 
graduated  into  parts  corresponding  to  the  beats  of  the 
Philadelphia  clock.  The  astronomer  at  Cambridge  now 
selects  a  convenient  star  for  observation,  and  announces 
it  by  name  to  each  of  the  other  stations.  He  strikes  the 
key  of  his  register  as  the  star  passes  successively  each 
wire  of  his  transit  instrument,  and  the  dates  are  printed 
not  only  upon  his  own  roll  of  paper,  but  also  upon  those 
at  New  York,  Philadelphia  and  Washington.  When 
the  same  star  comes  over  the  merfcian  of  New  York, 
the  observer  there  goes  through  the  same  operation,  and 
his  observations  are  printed  upon  all  four  of  the  papers. 
The  Philadelphia  observer  does  the  same  when  the  star 
comes  upon  his  own  meridian.  Thus  we  have  four  Jong 
rolls  of  paper,  one  at  Cambridge,  a  second  at  New  York, 
a  third  at  Philadelphia,  and  a  fourth  at  Washington,  all 
graduated  into  equal  parts  by  the  ticking  of  the  Phila- 
delphia clock,  and  upon  these  we  have  printed  the 
instants  at  which  the  star  was  seen  to  pass  each  wire  of 
the  transits  at  Cambridge,  New  York  and  Philadelphia. 
The  position  of  each  mark  thus  printed  shows  not  only 
the  second  of  occurrence,  but  also  the  fraction  of  a 


332  HISTOKY  OF  ASTKONOMY. 

second,  which  may  be  measured  with  scale  and  dividers. 
Thus,  if  we  suppose  the  transit  instruments  to  be  all  ad- 
justed to  the  meridian,  and  the  rate  of  the  clock  to  be 
correct,  we  have  obtained  the  difference  of  longitude  of 
the  stations  compared,  independently  of  the  tabular  place 
of  the  star  employed,  and  also  independently  of  the 
absolute  error  of  the  clock.  The  observers  now  read 
their  levels,  and  reverse  their  transit  instruments.  The 
Cambridge  astronomer  selects  a  second  star,  which  is 
telegraphed  in  the  same  manner  as  the  first.  Thus  the 
error  of  collimation  of  all  the  telescopes  is  corrected. 
The  other  errors  of  the  instruments  must  be  determined 
by  separate  observations  in  the  usual  manner.  Subse- 
quently a  third  and  a  fourth  star  were  selected  by  the 
Cambridge  astronomer,  and  telegraphed  in  the  same 
manner  as  they  passed  in  succession  over  the  different 
meridians.  These  feperiments  were  made  on  the  23d 
of  January,  1849,  and  occupied  most  of  the  night.  The 
results  were  most  wonderful,  and  have  opened  an  en- 
tirely new  field  of  investigation.  Hitherto  in  transit 
observations,  astronomers  had  been  accustomed  to  es- 
timate fractions  of  a  second  entirely  by  the  ear,  with 
only  such  assistance  from  the  eye  as  could  be  derived 
from  the  rapid  motion  of  the  star  through  the  field  of  the 
telescope.  The  error  of  such  an  observation,  even  with 
practiced  observers,  frequently  amounts  to  a  quarter  of 
a  second.  But  in  this  new  mode  of  observation,  the 
observer  has  no  use  for  his  ears.  The  astronomer 
might  in  future  be  made  without  ears.  It  is  only  nee- 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       333 

essary  for  him  to  move  his  fingers  at  the  instant  the 
star  is  seen  to  pass  each  wire  of  his  telescope,  and  his 
observation  is  recorded  in  a  permanent  form,  and  may 
be  subsequently  examined  at  his  leisure. 

During  the  months  of  July  and  August,  1849,  a  tele- 
graphic comparison  was  made  between  the  observa- 
tories of  Philadelphia,  and  Hudson,  Ohio.  Signals  were 
exchanged  on  three  different  nights,  the  results  of  which 
gave  the  difference  of  longitude  between  the  High  School 
observatory,  and  the  Hudson  observatory  25m.  5*7s. 
During  the  same  summer,  some  new  comparisons  were 
made  between  Philadelphia  and  Washington. 

On  the  5th  of  February,  1850,  a  perfect  telegraph  con- 
nection was  made  between  "Washington  and  Charleston, 
South  Carolina.  The  thermometer  at  Washington  was 
10°  Fahrenheit,  and  at  Charleston  28°  Fah.,  and  the  in- 
sulation of  the  wires  was  excellent.  Professor  Lewis  E. 
Gibbes  was  in  charge  of  the  operations  at  Charleston,  and 
the  operations  at  Washington  were  conducted  by  S.  C. 
Walker.  The  times  of  transit  of  a  full  series  of  zenith 
stars  were  telegraphed  between  Professor  Gibbes's  observ 
atory  and  Washington,  and  recorded  on  the  register  at 
each  station.  The  instruments  were  all  well  adjusted,  and 
all  necessary  precautions  taken  to  insure  satisfactory  re- 
sults. Signals  were  also  exchanged  on  the  llth  and 
12th  of  February,  but  the  results  were  not  so  satisfactory 
as  those  of  the  5th.  The  result  of  these  comparisons  in- 
dicates that  Charleston  is  llm.  45'27s.  west  of  Wash- 
ington. 


334:  HISTOBY  OF  ASTRONOMY. 

In  March,  1851,  the  difference  of  longitude  between 
Charleston  and  Savannah  was  determined  by  telegraph. 
At  the  Charleston  end,  the  observations  were  made  by 
Professor  Lewis  K.  Gibbes,  at  his  observatory ;  and  at  the 
Savannah  end  by  Mr.  C.  O.  Boutelle.  Thus  the  Seaton 
station  at  Washington  was  connected  with  Savannah,  the 
difference  of  longitude  between  Charleston  and  Washing- 
ton having  been  determined  in  the  operations  of  the  pre- 
vious year. 

In  December,  1851,  was  determined  the  difference  of 
longitude  between  Cambridge,  Mass.,  and  Bangor,  Maine ; 
and  also  between  Bangor  and  Halifax,  Nova  Scotia,  un- 
der the  general  direction  of  Professor  S.  C.  Walker. 
Professor  Bond,  of  Cambridge,  and  Captain  Shortland, 
of  the  British  Admiralty  Survey  of  Nova  Scotia,  had 
concerted  the  connection  of  these  two  places  by  the  tele- 
graph; and  it  was  considered  important  to  furnish  an 
intermediate  station  in  Maine,  and  to  connect  the  Survey 
of  the  United  States  with  the  British  Survey.  The 
operations  were  entirely  successful,  as  far  as  Cambridge 
and  Bangor  were  concerned,  but  the  number  of  signals 
exchanged  between  Bangor  and  Halifax  was  small. 

The  difference  of  longitude  between  Seaton  station,  at 
Washington,  and  Eoslyn  station,  near  Petersburg,  Ya., 
was  determined  by  observations  made  on  six  nights 
between  July  3  and  August  7,  1852.  The  chief  object 
in  these  observations  was  to  examine  the  influence  of  the 
different  circumstances  producing  errors  in  the  longitude 
determinations  by  this  method.  In  determining  the 


APPLICATION  OF  THE  ELECTRIC  TELEGEAPH.       335 

difference  of  longitude,  one  hundred  and  twenty-four  ob- 
servations were  made  upon  thirty-five  zenith  stars; 
eighteen  observations  for  collimation  and  nine  for 
equatorial  intervals  were  made  upon  three  circumpolar 
stars.  In  connection  with  these  operations,  one  hundred 
and  twenty-two  observations  were  made  upon  twelve 
stars  for  local  time.  The  instrument  employed  was  a 
forty-three  inch  transit  instrument ;  the  diaphragm  con- 
sisted of  twenty-five  wires  arranged  in  groups  of  five. 
The  result  of  these  observations  shows  Petersburg  to  be 
1m.  35'603s.  west  of  Washington,  with  a  probable  error 
of  +_  0*009s.  The  probable  error  of  a  single  set  of  ob- 
servations of  a  star  over  fifteen  wires  is  _+_  OOSls.  The 
residual  probable  error  of  a  single  night's  work,  with 
the  transits  of  fifteen  stars  telegraphed  from  and  received 
at  both  stations,  not  accounted  for  by  the  error  of  tap- 
ping and  receiving,  is  but  O004s.,  or  may  be  considered 
insensible,  so  that  it  is  unnecessary  to  multiply  the  num- 
ber of  nights  of  observation. 

During  the  winter  of  1852  and  '53,  a  second  determi- 
nation of  the  difference  of  longitude  between  Charleston, 
South  Carolina,  and  the  Seaton  station  in  Washington 
was  attempted  under  the  direction  of  Dr.  B.  A.  Gould 
From  the  middle  of  December  until  the  middle  of  Feb- 
ruary, Dr.  Grould  remained  in  Charleston,  observing  on 
every  fair  night  circumpolar  stars  with  reversals,  and 
both  zenith  and  equatorial  stars  chrpnographically,  for 
the  determination  of  time  and  instrumental  corrections. 
Whenever  the  sky  was  unclouded  both  at  Washington 


336'  HISTORY  OF  ASTRONOMY. 

and  Charleston,  the  batteries  were  set  up,  and  the  greater 
part  of  the  night  spent  in  attempts  to  obtain  direct  com- 
munication between  the  two  places.  After  a  series  of  the 
most  varied  experiments,  the  operators  were  forced  to  the 
conclusion  that  the  condition  of  the  telegraph  wires  was 
such  that  direct  telegraphic  communication  between  the 
two  stations  was  impossible.  It  thus  became  necessary 
to  establish  an  intermediate  station :  and  one  was  accord- 
ingly erected  at  Baleigh,  North  Carolina.  It  was  here 
found  that  direct  communication  both  with  Washington 
and  Charleston  was  possible.  The  series  of  observations 
was  completed  on  the  14th  of  May,  1853,  at  which  time 
eighty-four  transits  of  stars  had  been  exchanged  with 
Washington  on  four  nights ;  and  fifty-nine  exchanged 
with  Charleston  on  four  nights. 

During  the  winter  of  1853  and  '54,  the  longitude  experi- 
ments were  renewed  under  the  direction  of  Dr.  Gould. 
On  account  of  the  telegraph  facilities,  it  appeared  de- 
sirable that  Columbia,  South  Carolina,  rather  than 
Charleston  should  form  a  link  in  the  great  chain  of 
telegraphic  longitude-stations  which  are  to  connect  the 
north-eastern  with  the  south-western  sea-ports  of  the 
United  States,  and  a  station  was  accordingly  selected  at 
Columbia.  The  observations  at  Columbia  were  made  by 
Dr.  Gould  and  those  at  Raleigh  by  Mr.  G.  W.  Dean.  It 
was  Dr.  Gould's  intention  to  push  the  longitude  con- 
nections as  far  as  Macon,  Gorgia,  and  an  astronomical 
station  was  also  selected  in  that  city,  but  the  unfavorable 
state  of  the  weather  prevented  his  occupying  that  station. 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       337 

The  observations  were  commenced  at  Columbia,  January 
4,  1854,  but  no  opportunity  for  exchanging  signals  with 
Ealeigh  could  be  obtained  until  January  21st.  It  was 
not  until  the  llth  of  February,  that  three  good  series  of 
star  signals  had  been  exchanged.  Dr.  Gould  then  took 
charge  of  the  station  at  Ealeigh,  while  Mr.  Dean  went  to 
Columbia,  and  on  the  12th  of  March,  they  succeeded  in 
completing  the  second  series  of  three  nights'  satisfactory 
exchange  of  signals. 

The  season  being  too  far  advanced  for  the  proposed 
connection  of  Columbia  and  Macon,  the  Columbia  instru- 
ments were  removed  to  Wilmington,  North  Carolina,  and 
those  at  Ealeigh  to  Eoslyn  station  near  Petersburg,  Ya., 
and  the  observations  for  the  connection  of  these  two 
places  commenced  with  the  month  of  May.  Star  signals 
were  exchanged  between  Mr.  Pourtales  at  Petersburg  and 
Mr.  Dean  at  Wilmington  on  the  27th  of  May  and  6th  of 
June,  when  they  exchanged  stations,  and  again  worked 
successfully  on  the  20th  and  23d  of  June. 

In  January  and  February,  1855,  observations  were 
made  to  determine  the  difference  of  longitude  between 
Cambridge,  Mass.,  and  Fredericton,  New  Brunswick. 
It  was  originally  intended  to  have  an  unbroken  telegraph 
communication  between  the  Fredericton  observatory 
and  that  of  Harvard  University,  but  in  consequence  of 
the  wires  from  the  latter  to  the  office  in  Boston  being  out 
of  repair,  Professor  Bond  found  it  necessary  to  trust  to 
two  sidereal  chronometers  for  the  interval.  The  chro- 
nometers were  carefully  and  repeatedly  compared  with 

15 


338  HISTORY  OF  ASTRONOMY. 

the  transit  clock  at  Cambridge,  both  before  and  after  in- 
terchanging signals,  so  as  to  ascertain  their  error  and 
rate ;  and  at  both  observatories,  on  each  day  of  operations, 
the  meridian  passages  of  a  number  of  stars  were  observed, 
in  order  to  obtain  the  error  and  rate  of  the  transit  clocks. 
The  method  of  operation  was  as  follows :  The  assistant 
at  Boston  commenced  at  an  even  minute  by  his  chro- 
nometer, and  sent  second-beats  for  fifty  consecutive 
seconds.  This  was  continued  for  ten  successive  minutes, 
beginning  always  at  the  even  minute,  and  the  times  were 
noted  by  the  transit  clock  at  Fredericton.  Sub- 
sequently the  observers  at  Fredericton  took  the  initia- 
tive and  sent  a  series  of  signals  to  Boston.  The  following 
are  the  results  of  these  comparisons : 

1855,  Jan.  23.   Longitude  by  signals  sent  from  B.  to  F.     17m.  57-38s. 
Feb.  2. 


Feb.  10. 


Result  of  all  the  comparisons  17m.  5  7  -23s. 

During  the  winter  of  1854-5,  the  telegraph  operations 
for  longitude  were  extended  as  far  as  Macon,  Ga.,  and 
arrangements  were  made  for  continuing  the  work  to 
Montgomery  and  Mobile.  In  December,  1854,  Dr. 
Gould,  assisted  by  Mr.  Goodfellow,  occupied  the  ob- 
servatory at  Columbia,  S.  C.,  and  Mr.  Dean  took  charge 


F.  to  B. 

57  -30s. 

F.  to  B. 

57-SOs. 

B.  to  F. 

57-20s. 

F.  to  B. 

67-14s. 

B.  to  F. 

57-19s. 

F.  to  B. 

67  -19s. 

B.  to  F. 

57-19s. 

APPLICATION   OF  THE  ELECTRIC  TELEGRAPH.       339 

of  the  station  at  Macon.  After  successful  exchanges  of 
signals  on  three  different  nights,  Messrs.  Dean  and  Grood- 
fellow  interchanged  stations,  and  obtained  exchanges  on 
three  more  nights  with  satisfactory  results.  The  series 
of  astronomical  observations  extended  from  December 
30th  to  March  16th.  The  clocks  employed  were  adapted 
to  the  chronographic  method  of  observation  by  Mr. 
Saxton.  The  spring  governor  and  Kerrison  regulator 
were  used  for  the  chronographic  registry  of  the  transit 
observations;  but  during  the  exchange  of  telegraphic 
signals,  an  ordinary  Morse  register  was  also  employed 
at  each  station,  and  was  found  to  give  results  com- 
parable in  accuracy  with  either  of  the  former,  owing  to 
the  greater  length  of  the  seconds  as  recorded  upon  the 
fillet,  and  to  the  general  uniformity  maintained  during 
any  change  of  rate. 

During  the  winter  of  1855-6,  a  comparison  was  made 
between  Wilmington,  N.  C.,  and  Columbia,  S.  C.,  by  means 
of  a  new  telegraph  line,  which  gives  one  determination  of 
longitude  between  Petersburg  and  Columbia  by  the  way 
of  Kaleigh,  and  another  by  the  way  of  Wilmington.  Sig- 
nals were  also  exchanged  between  Macon  and  Montgom- 
ery, Ala.  Preliminary  arrangements  have  been  made 
at  Mobile  for  the  next  season's  work,  and  the  station 
at  New  Orleans  has  been  selected.  The  arrangements 
for  determining  the  difference  of  longitude  between  New 
Orleans  and  the  observatories  along  the  eastern  coast 
of  the  United  States  are  therefore  fast  approaching 
their  completion. 


340  HISTOEY  OF  ASTRONOMY. 

The  following  are  the  rules  now  adopted  in  the  Coast 
Survey  operations  for  longitude.  After  the  operators 
have  connected  the  observatories  and  adjusted  their 
magnets,  so  that  the  two  stations  receive  each  other's 
writing  well  with  the  least  possible  pass,  the  clock  of 
the  most  eastern  station  is  put  on.  The  observer  at  the 
other  station  then  strikes  a  dot  each  alternate  second, 
until  the  observer  at  the  clock  station  signifies  "Aye, 
aye,"  by  double  dots,  each  alternate  second.  The  ex- 
change of  signals  then  begins  as  follows : 

First  star. 

Beading  of  level. 
Second  star. 

Eeversal  of  instrument. 
Third  star. 

Beading  of  level, 
etc.  etc. 

In  general  it  is  only  desirable  to  observe  on  the  three 
middle  tallies.  The  observer  always  informs  the  re- 
corder of  the  tallies  observed,  and  of  any  lost  or  badly 
struck  threads.  When  ten  stars  have  been  satisfactorily 
exchanged,  the  eastern  clock  is  taken  off  the  circuit,  and 
the  western  clock  put  on ;  and  the  exchange  of  ten  stars 
more  completes  the  telegraphic  work  for  the  night.  A 
good  determination  of  the  instrumental  corrections  after 
the  close  of  telegraph  work,  is  far  preferable  to  any  in- 
crease of  the  number  of  star  exchanges  above  twenty. 

When  fifty  stars  .have  been  satisfactorily  exchanged, 
and  on  not  less  than  three  nights,  the  observers  ex- 


APPLICATION  OF  THE  ELECTKIC  TELEGRAPH.       341 

change  stations,  leaving  the  transit  instrument  and  clock 
as  before,  meeting,  however,  on  one  night  to  observe  for 
personal  equation.  Fifty  stars  are  then  to  be  exchanged 
again  on  not  less  than  three  nights,  in  the  new  position 
of  the  observers,  and  a  new  series  of  observations  made 
for  personal  equation. 

APPLICATION  OF  THE  ELECTRIC  CIRCUIT  TO  ASTRONOMICAL 
OBSERVATIONS. 

It  is  obvious  that  the  electric  circuit,  as  it  has  been 
employed  in  the  determination  of  longitude,  may  also 
be  employed  in  the  ordinary  business  of  an  astronomical 
observatory.  When  Professor  Locke  invented  his 
electro-chronograph,  by  which  the  electric  circuit  was 
broken,  and  dots  were  printed  on  paper  every  second 
by  the  action  of  a  clock,  Mr.  Walker  and  many  others 
anticipated  that  this  would  immediately  supersede  the 
old  method  of  observing  transits  of  stars.  This  new 
method  of  observation  has  a  great  advantage  over  the 
old  in  respect  of  accuracy.  Astronomers  have  hitherto 
measured  small  intervals  of  time  by  listening  to  the 
beats  of  a  clock  or  chronometer,  and  estimating,  as  well 
as  they  were  able,  the  fraction  of  a  second  when  any 
event  has  occurred,  such  as  an  occultation  of  a  star,  or 
the  transit  of  a  star  over  the  wires  of  a  telescope.  The 
ear  is,  however,  a  very  imperfect  organ.  While  the  eye 
readily  estimates  a  fraction  of  a  line  with  the  precision 
of  a  tenth,  the  ear  seldom  distinguishes  smaller  portions 
of  an  interval  of  time  than  a  fifth.  In  the  opinion  of 


342  HISTOKY  OF  ASTRONOMY. 

Mr.  Walker,  the  error  in  the  mechanical  part  of  imprint- 
ing a  date  on  the  automatic  clock  register,  and  in  reading 
off  the  record,  need  not  exceed  a  hundredth  part  of  a 
second.  Mr.  "Walker  estimates  that  a  transit  over  one 
wire,  printed  by  the  new  method,  is  worth  four  wires 
observed  by  the  old  method. 

Another  advantage  of  the  new  method  of  observation 
arises  from  the  increased  amount  of  work  which  can  be 
done  in  a  given  time.  Fifteen  seconds  is  the  ordinary 
equatorial  interval  for  the  wires  of  a  transit  instrument. 
In  the  new  method  of  observing,  the  equatorial  intervals 
may  be  reduced  from  fifteen  to  two  seconds,  or  even  to 
one  and  a  half.  In  this  manner  the  number  of  bisections 
in  a  single  culmination  of  a  star  may  be  multiplied  ten 
fold,  making  a  gain  of  forty  fold  by  the  new  or  automatic 
method.  This  is  the  estimated  gain  from  the  multipli- 
cation of  transits  over  wires,  and  the  superior  precision 
of  each.  There  are,  however,  other  circumstances  which 
detract  from  this  advantage,  such  as  the  time  required  to 
prepare  the  apparatus  for  observation,  to  transcribe  the 
printed  record  into  figures,  etc. 

Before,  however,  the  full  advantage  of  this  method 
could  be  realized,  some  practical  difficulties  remained  to 
be  overcome,  of  which  the  most  important  were  the  two 
following : 

1st.  It  was  essential  to  the  accuracy  of  the  new  method 
that  the  fillet  of  paper,  or  whatever  might  be  the  surface 
upon  which  the  dots  were  registered,  should  be  made 
to  advance  with  perfectly  uniform  motion  ;  and 


APPLICATION   OF  THE  ELECTRIC  TELEGRAPH.       343 

2d.  It  was  very  important  that  the  register  should  not 
merely  secure  accuracy,  but  should  also  be  reduced  to  a 
compact  and  convenient  form. 

The  first  condition,  that  of  uniform  motion  of  the 
fillet  of  paper,  was  very  far  from  being  secured  with 
the  ordinary  telegraph  apparatus.  .In  this  apparatus, 
the  only  arrangement  for  producing  uniform  motion 
consists  of  a  fly,  which,  revolving  with  great  rapidity, 
and  meeting  resistance  from  the  air,  opposes  the  descent 
of  the  moving  weight.  Now,  when  in  telegraphing,  the 
graver  is  pressed  against  the  surface  of  the  paper,  the 
friction  of  the  machinery  is  increased,  and  by  this  means 
the  velocity  of  the  paper  is  diminished,  and  the  press- 
ure may  easily  be  increased  so  as  to  stop  the  motion 
entirely.  The  very  operation,  therefore,  of  registering 
dots  on  the  paper,  introduces  an  irregularity  in  the 
motion  of  the  fillet.  Now,  it  is  indispensable  to  the 
proposed  use  of  the  apparatus,  that  the  electric  circuit 
should  be  closed  during  the  principal  part  of  every 
second;  for,  when  the  circuit  is  open,  it  is  not  in  the 
power  of  the  operator  to  print  a  dot  on  the  paper. 
The  result  was,  that  when  Dr.  Locke's  clock  came  to 
be  used  in  connection  with  the  Morse  registering  ap- 
paratus, the  graver  was  kept  pressed  against  the  fillet  of 
paper  about  nine-tenths  of  every  second,  by  which  means 
the  motion  of  the  fillet  was  rendered  very  slow  and 
irregular;  but  as  soon  as  the  circuit  was  broken,  the 
paper  moved  forward  as  by  a  sudden  impulse.  The  first 
improvement  consisted  in  reversing  the  action  of  the 


3M  HISTORY  OF  ASTRONOMY. 

graver,  so  that  when  the  circuit  was  complete,  the  paper 
was  entirely  free,  and  a  dot  was  made  "by  the  breaking 
of  the  circuit.  The  paper  graduated  into  seconds  by 
this  arrangement,  exhibited  dots  with  long  intervening 
spaces,  as  shown  on  page  325. 

It  was  still  necessary  to  introduce  some  nicer  ap- 
paratus for  regulating  the  motion  of  the  surface  upon 
which  the  dots  were  to  be  registered.  Professor  Mitchell 
causes  his  registering  disc  to  revolve  with  a  uniform  motion 
by  connecting  it  with  the  driving  apparatus  of  his  Mu- 
nich equatorial.  Professor  Locke  prefers,  for  the  moving 
power,  a  centrifugal  clock.  Professor  Bond  employs  a 
machine  of  his  own  invention,  called  the  spring  gov- 
ernor, and  described  on  page  324.  Professor  Airy,  of 
Greenwich,  employs  a  large  conical  pendulum,  revolving 
in  a  circle,  the  diameter  of  which  is  about  equal  to  the 
arc  of  vibration  of  an  ordinary  second's  pendulum* 

Mr.  Saxton's  arrangement  of  registering  upon  a  sheet 
of  paper  wound  round  a  cylinder,  is  the  most  con- 
venient which  has  been  hitherto  employed. 

The  electric  method  of  recording  transits  has  been 
employed  at  the  Washington  observatory  exclusively 
since  December,  1849  ;  it  was  introduced  soon  afterward 
at  the  Cambridge,  Mass.,  observatory,  and  it  is  now  used 
also  at  the  Greenwich  observatory. 


APPLICATION  OF  THE  ELECTEIC  TELEGRAPH.       345 

APPLICATION  OF  THE  ELECTRIC  CIRCUIT  TO  ASTRONOMICAL 
USES  IN  EUROPE. 

In  December,  1849,  the  astronomer  royal  of  England 
communicated  to  the  Koyal  Astronomical  Society  a 
detailed  account  of  "the  method  of  observing  and  re- 
cording transits  lately  introduced  in  America;"  and  he 
concluded  his  narrative  by  stating  that  the  possible  advan- 
tages of  this  method  appeared  so  great,  that  he  had  begun 
to  contemplate  the  practicability  of  adopting  it  in  the  Koyal 
observatory.  He  proposed  to  record  the  observations 
upon  a  cylinder,  perhaps  revolving  upon  a  screw  axis ; 
and  suggested  that  great  convenience  would  be  gained 
if  the  movement  of  the  cylinder  could  be  made  so  per- 
fectly uniform  that  it  could  be  adopted  as  the  transit 
clock.  He,  therefore,  urged  strongly  the  importance  of 
improvements  of  the  centrifugal  or  conical  pendulum 
clock,  as  the  only  instrument  yet  made  which  is  able  to 
do  heavy  work  with  smooth  motion,  and  with  an  ac- 
curacy at  present  so  great  as  to  make  it  probable  that, 
with  due  modification,  the  greatest  accuracy  may  be  ob- 
tained. 

In  June,  1853,  Professor  Airy  reported  that  owing  to 
various  delays  his  apparatus  was  not  yet  brought  into 
use ;  but  that  he  had  brought  it  to  such  a  state,  that  he 
was  beginning  to  try  whether  the  barrel  moved  with  suffi- 
cient uniformity  to  be  itself  used  as  the  transit  clock. 

The  first  transits  recorded  by  the  electric  method  at 

Greenwich  were  made  on  March  27,  1854,  and  since  that 

15* 


346  HISTORY  OF  ASTRONOMY. 

time  all  the  transits,  with  trifling  interruptions,  have  been 
made  by  the  same  agency,  except  for  the  very  slow 
circumpolar  stars,  for  which  they  use  the  same  wires,  but 
by  observation  with  eye  and  ear.  The  paper  on  which 
the  punctures  are  to  be  made  is  folded  in  a  wet  state 
upon  a  brass  cylinder  covered  with  a  single  thickness 
of  woolen  cloth,  and  has  its  edges  united  by  glue. 

The  punctures  are  produced  by  two  systems  of 
prickers,  which  have  nothing  in  common,  except  that 
they  are  carried  by  the  same  traveling  frame  which 
moves  slowly  in  the  direction  of  the  barrel  axis,  while 
the  barrel  revolves  beneath  it.  One  pricker  is  driven  by 
a  galvanic  magnet,  whose  galvanic  circuit  is  completed 
at  every  second  of  sidereal  time.  Professor  Airy  at  first 
intended  that  the  completion  of  the  circuit  should  be 
effected  by  the  same  clock  (regulated  by  a  conical  pen- 
dulum) which  drives  the  barrel.  He  found,  however, 
that  he  could  not  insure  such  a  constancy  in  the  arc  of 
the  pendulum  as  would  make  its  rate  sufficiently  uniform 
to  entitle  it  to  be  considered  as  the  fundamental  clock. 
He  therefore  carried  wires  from  the  pricker  magnet  to 
the  transit  clock,  and  connected  them  with  springs  whose 
contact  is  made  at  every  second  by  the  transit  clock.  A 
wheel  of  60  teeth  is  fixed  on  the  escape-wheel  axis,  and 
the  teeth  of  this  wheel  in  succession  make  momentary 
contacts  of  the  galvanic  springs.  The  position  of  the 
springs  is  so  adjusted  that  the  effort  of  the  wheel-tooth 
upon  them  occurs  only  when  one  escape-tooth  has  passed 
the  sloping  surface  of  the  pallet,  and  the  other  escape- 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.         347 

tooth  is  dropping  upon  its  bearing ;  so  that  the  resistance 
of  the  springs  does  not  affect  the  legitimate  action  of  the 
train  upon  the  pendulum. 

The  other  pricker  is  driven  by  a  galvanic  magnet, 
whose  circuit  is  completed  by  an  arbitrary  touch  made 
by  an  observer's  finger  upon  a  contact  piece.  There  are 
three  contact  pieces.  One  is  upon  the  eye  end  of  the 
transit  circle ;  the  other  two  are  upon  the  base  plate  of 
the  altazimuth,  one  to  be  used  *with  vertical  face  to  the 
right,  the  other  with  vertical  face  to  the  left.  Thus  alt- 
azimuth observations  are  referred  absolutely  to  the  same 
time  record  as  transit  circle  observations. 

It  is  necessary  to  mark  upon  the  revolving  barrel  the 
beginnings  of  some  minutes ;  and  the  numeration  of  some 
hours  and  minutes.  This  is  done  by  arbitrary  punctures, 
given  by  the  observer's  touch.  In  order  to  guide  the  eye 
through  the  multitude  of  dots  upon  the  sheet,  lines  of  ink 
are  traced  by  means  of  a  glass  pen,  which  is  attached 
to  the  same  frame  as  that  by  which  the  prickers  are 
carried. 

"Wires  have  been  inserted  in  the  wire-plates,  both  of 
the  transit  circle  and  of  the  altazimuth,  at  intervals 
adapted  to  the  rapid  observation  by  touch.  The  wires 
of  the  transit  circle,  and  the  vertical  wires  of  the  altazi- 
muth are  adapted  to  intervals  of  about  42*  and  48*  of 
arc ;  the  intervals  of  the  horizontal  wires  of  the  altazi- 
muth do  not  exceed  24"  of  arc.  These  are  probably  the 
smallest  intervals  that  have  ever  been  used  for  similar 
observations.  The  old  systems  of  wires  are  not  dis- 


348  HISTORY  OF  ASTRONOMY. 

turbed  nor  rendered  confused;  so  that  with  the  transit 
circle,  either  7  wires  may  be  observed  by  ear,  or  9  by 
touch ;  and  with  the  altazimuth,  either  6  by  ear  or  6  by 
touch. 

Professor  Airy  remarks  that  this  apparatus  is  now 
generally  efficient.  It  is  troublesome  in  use  :  consuming 
much  time  in  the  galvanic  preparations,  the  preparation 
of  the  paper,  and  the  translation  of  the  puncture  indica- 
tions into  figures.  But  among  the  observers  who  use  it, 
there  is  but  one  opinion  on  its  astronomical  merits — that, 
in  freedom  from  personal  equation  and  in  general  ac- 
curacy, it  is  very  far  superior  to  the  observations  by  eye 
and  ear. 

Electro-magnetic  registering  apparatus  has  also  been 
introduced  by  Dr.  Lamont  at  the  Munich  observatory 
and  is  described  in  the  work,  "  Beschreibung  der  an 
der  Miinchener  Sternwarte  zu  den  Beobachtungen  ver- 
wendeten  neuen  Instrumente  und  Apparate  von  Dr.  La- 
mont, Munchen,  1851." 

It  is  not  known  that  the  American  method  of  observ- 
ing has  been  introduced  into  any  other  observatories  of 
Europe ;  but  M.  Leverrier,  the  Director  of  the  Imperial 
observatory  of  Paris,  has  recently  drawn  up  a  Eeport  in 
which  he  recommends  to  construct  a  large  meridian 
circle,  and  to  economise  the  resources  presented  by 
dynamical  electricity,  in  order  to  assure  to  the  observa- 
tions all  the  precision  of  which  they  are  susceptible. 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       849 

EXPERIMENTS  MADE  IN  EUROPE  FOR  THE  DETERMINA- 
TION OF  GEOGRAPHICAL  LONGITUDE  BY  THE 
ELECTRIC  TELEGRAPH. 

During  the  summer  of  1852,  the  Royal  observatory  at 
Greenwich  was  put  in  galvanic  communication  with  the 
principal  telegraph  offices  in  London,  for  the  purpose  of 
determining  differences  of  longitude  with  other  observa- 
tories, British  and  continental.  The  first  comparison 
was  made  between  the  observatories  of  Greenwich  and 
Cambridge.  The  electric  current  was  made  to  pass 
through  the  coils  of  a  telegraph  needle  at  Greenwich, 
and  through  the  coils  of  another  telegraph  needle  at 
Cambridge,  so  that  the  completion  of  the  circuit  at  Green- 
wich produced  a  movement  both  in  the  needle  at  Green- 
wich and  in  that  at  Cambridge.  The  order  of  operations 
was  as  follows : 

At  11  P.M.,  Greenwich  mean  solar  time,  Greenwich 
commenced  by  giving  five  signals  at  intervals  of  about  2 
seconds  each.  The  turn-plates  were  changed,  and  Cam- 
bridge responded  by  five  similar  signals.  These  were 
merely  to  say  "All  is  right."  Greenwich  then  gave 
groups  of  signals  at  intervals  of  10s.  to  15s.,  in  numbers 
of  from  three  to  nine  signals  in  a  group  (some  of  them 
being  transits  of  stars)  to  llh.  15m.  Notice  was  pre- 
viously given  of  the  number  of  signals  to  be  expected  in 
each  group,  by  giving  the  same  number  of  warning  signals 
at  intervals  of  about  two  seconds.  Then  Cambridge  gave 
similar  groups  of  signals  to  llh.  30m.  Then  Greenwich 


350  HISTORY  OF  ASTRONOMY. 

gave  signals  to  llh.  45m.,  and  Cambridge  to  12h.  Om. 
This  closed  the  night's  signals.  From  135  to  150  efficient 
signals  were  given.  The  evenings  selected  for  the  deter- 
mination of  the  longitude  of  Cambridge  were  those  of 
May  17  and  18, 1853.  On  May  17,  Mr.  Dunkin  observed 
transits  and  galvanic  signals  at  Greenwich,  and  Mr.  Todd 
observed  at  Cambridge.  On  the  morning  of  the  18th, 
the  observers  were  interchanged,  and  Mr.  Todd  observed 
transits  and  signals  at  Greenwich,  while  Mr.  Dunkin  ob- 
served at  Cambridge.  The  errors  of  the  transit  clock 
were  determined  by  two  methods  :  method  (A)  in  which 
the  Nautical  Almanac  stars  were  employed,  but  no  par- 
ticular care  was  taken  for  the  identity  of  the  stars  at  the 
two  stations;  and  method  (B)  in  which  the  same  stars 
were  observed  at  both  stations,  but  no  attention  was 
given  to  the  accuracy  of  the  assumed  right  ascensions. 

For  comparison  of  the  Cambridge  transit  clock,  with 
the  chronometers  used  at  the  railway  stations,  Professor 
Challis  employed  three  chronometers.  It  was  found 
necessary  to  reject  the  comparisons  of  one  of  them. 

The  results  of  these  operations  were  as  follows : 

Method  (A).     Method  (B). 

May  17, by  146  signals,  East  longitude  of  Cambridge  22-660s.        22-601s. 
May  18,  by  135  signals,  "  22-713S.        22'782s. 

Mean     22'687s.        22'691s. 
Mean  of  the  whole  22 -689s. 

The  result  arrived  at  in  1829  by  transmission  of  chro- 
nometers was  23*54:3. 


APPLICATION  OP  THE  ELECTRIC  TELEGRAPH.        351 

On  May  25,  1853,  signals  were  passed  in  the  same 
manner  to  and  from  Edinburg,  for  the  determination  of 
the  longitude  of  Edinburg  observatory.  In  these  com- 
parisons the  following  result  was  obtained,  that  when  a 
signal  is  given  at  Greenwich  by  means  of  a  Greenwich 
battery,  the  time  noted  for  the  signal  at  Edinburg  is  later 
than  that  noted  at  Greenwich  by  T*T  of  a  second  of  time, 
and  vice  versa,  if  the  signal  is  given  at  Edinburg  by  means 
of  an  Edinburg  battery.  This  difference  Professor 
Airy  ascribes  to  two  causes ;  first,  the  time  actually  oc- 
cupied by  the  transmission  of  the  galvanic  pulse,  which 
according  to  the  American  determination,  would  explain 
less  than  half  of  the  difference ;  secondly,  the  circum- 
stance that  the  galvanic  current  when  it  reaches  the 
distant  needle  is  somewhat  less  vigorous  than  when  it 
passes  the  nearer  needle,  and  the  languid  movement  of 
the  distant  needle  catches  the  eye  more  slowly  and  is  re- 
corded as  occurring  at  a  later  time. 

In  August,  1853,  observations  were  made  to  determine 
the  difference  of  longitude  between  the  observatory  at 
Berlin  and  that  at  Frankfort  on  the  Maine.  M.  Encke 
and  Dr.  Briinnow  observed  at  the  former  station,  and  Dr. 
Lorey  at  the  latter.  The  telegraph  apparatus  employed 
was  Morse's.  It  was  agreed  that  Dr.  Lorey  should  an- 
nounce by  signal  when  the  experiments  were  about  to 
commence,  after  which  he  was  to  make  a  series  of  signals 
during  the  next  ten  minutes,  it  being  arranged  that  he 
was  to  make  a  new  signal  about  the  beginning  of  each 
successive  minute.  M.  Encke  observed  the  corresponding 


352  HISTORY  OF  ASTKONOMY. 

time  at  the  telegraph  office  in  Berlin,  upon  a  mean  solar 
chronometer,  while  Dr.  Briinnow  made  similar  observa- 
tions upon  a  sidereal  chronometer.  The  ten  signals 
being  observed,  Dr.  Briinnow  gave  a  signal  from  Berlin 
to  announce  that  a  new  set  of  experiments  was  about  to 
commence,  and  this  was  followed  by  ten  successive  sig- 
nals as  before.  The  following  is  the  result  for  the  lon<- 
gitude  of  Frankfort  west  of  Berlin : 

SIGNALS  FROM  FRANKFORT. 

August  12,  18m.  51-79s.  Encke.  18m.  51-728.  Briinnow. 

28,  61-718.  61-858. 

18m.  51-758.  18m.  51.79s. 

Mean  18m.  51'7  7s. 

SIGNALS  FROM  BERLIN. 

August  12,             18m.  51.57s.  Encke.              18m.  51-92s.  Brunnew. 
28,  51-918.  5213s. 

18m.  61-748.  18m.  62'03s. 

Mean  18m.  51-89s. 

or  on  the  whole,  a  mean  difference  of  longitude  amount- 
ing to  18m.  51 '83s.  The  difference  of  the  two  results 
can  not  arise  from  the  circumstance  that  the  transmission 
of  the  signals  is  not  instantaneous,  since  during  the  in- 
terval of  transmission,  the  Frankfort  signals  ought  to 
have  arrived  -  too  late  at  Berlin,  in  which  case  the  differ- 
ence of  longitude  should  have  turned  out  too  great ; 
while  the  Berlin  signals  by  arriving  too  late  at  Frank- 
fort should  have  indicated  the  difference  of  longitude  too 
small.  In  reality,  however,  the  Berlin  signals  made  the 
west  longitude  greater  than  its  true  value.  These  experi- 
ments consequently  indicate  that  with  the  means  of  ob- 


APPLICATION  OF  THE  ELECTKIC  TELEGRAPH.       353 

servation  here  employed,  the  velocity  of  the  electric 
current  is  insensible  for  the  distance  between  Berlin  and 
Frankfort ;  a  distance  which,  by  the  circuitous  route  of  the 
telegraph,  amounts  to  about  300  English  miles. 

In  November,  1853,  the  difference  of  longitude  be- 
tween the  observatories  of  Greenwich  and  Brussels  was 
determined  by  means  of  the  electric  telegraph.  A  gal- 
vanic telegraph  needle  was  mounted  in  the  observatory 
at  Brussels  in  close  proximity  to  the  transit-clock,  nearly 
as  in  the  Greenwich  observatory.  The  signals  to  be 
made  were  simple  deviations  of  the  needle,  produced 
directly  by  the  galvanic  current  through  the  long  com^ 
municating  wire. 

It  was  arranged  that  the  observations  should  be  divided 
into  two  series :  that  in  the  first  series  an  observer  from 
Brussels  (M.  Bouvy)  should  observe  both  the  galvanic 
signals  and  the  transits  for  correcting  the  transit  clock  at 
Greenwich,  while  an  observer  from  Greenwich  (Mr.  Dun- 
kin)  made  the  corresponding  observations  at  Brussels ; 
that  this  series  should  be  continued  till  satisfactory  ob- 
servations had  been  obtained  upon  at  least  three  even- 
ings ;  that  the  observers  should  then  be  reversed,  and  the 
second  series  be  observed  in  the  same  manner.  The 
signals  were  to  occupy  one  hour  in  each  evening,  from 
lOh.  to  llh.  Brussels  mean  solar  time,  each  hour  being 
divided  into  four  quarters.  The  contacts  of  wires  for 
completing  galvanic  circuit  were  to  be  made  at  Green- 
wich and  with  a  Greenwich  battery  in  the  first  and  third 
quarters,  and  at  Brussels  with  a  Brussels  battery  in  the 


354  HISTORY  OF  ASTRONOMY. 

second  and  fourth  quarters  ;  and  between  the  two  sets  of 
observations  at  each  place  the  poles  of  the  battery  were 
to  be  reversed. 

The  transit  clocks  were  corrected  by  two  distinct 
methods  in  the  same  manner  as  in  the  operations  for  de- 
termining the  longitude  of  Cambridge. 

The  final  results  for  the  difference  of  longitude  as 
determined  by  the  two  methods  A  and  B  are  the 
following : 

Method  A.  Method  B. 

Mean  of  the  first  series           17m.  29 -256s.  17m.  29 -340s. 

"      second  series                    28'538s.  28-4763. 

Mean  of  the  two  series           17m.  28-897s.  17m.  28'908s. 

These  determinations  rest  upon  1104  signals.  The 
last  result  17m.  28'9s.  is  the  best  that  can  be  given  for 
the  difference  of  longitude  of  the  two  observatories.  It 
is  however  remarkable  that  the  difference  of  the  results 
given  by  the  two  series  is  O791s.,  which  is  probably  due 
to  personal  equation  of  the  observers. 

The  time  employed  by  the  galvanic  current  in  passing 
between  the  two  observatories,  a  distance  of  270  miles,  is 
0'109s.,  which  indicates  a  velocity  of  only  2500  miles  per 
second.  It  is  however  to  be  remarked,  that  from  Green- 
wich to  London  and  thence  to  Ostend,  the  whole  of  the 
line  is  subterraneous  or  sub-aqueous,  and  it  is  considered 
probable  that  the  observed  retardation  belongs  almost 
entirely  to  this  portion  of  the  line. 

In  May  and  June,  1854,  the  difference  of  longitude 
between  Greenwich  and  Paris  observatories  was  deter- 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       355 

mined ;  and  the  arrangements  adopted  were  the  same  as 
had  been  previously  tried  between  Greenwich  and  Brus- 
sels. Mr.  Dunkin,  assistant  at  Greenwich  observatory 
went  to  Paris,  and  M.  Faye,  assistant  at  the  Paris  ob- 
servatory, went  to  Greenwich,  and  the  comparisons 
commenced  the  27th  of  May.  The  second  series  of 
observations  commenced  June  12th,  and  were  made  by 
Mr.  Dunkin  at  Greenwich  and  by  M.  Faye  at  Paris. 
The  final  results  for  the  difference  of  longitude  as 
determined  by  the  two  methods  A  and  B  are  the 
following : 


FIRST    SERIES. 


Number  of  signals.        Method  A. 

Method  B. 

1854,  May  27, 

146,                 9m.  20-403. 

9m.  20-383. 

"    29, 

146,                         20-59s. 

20-563. 

"     31, 

147,                       20-543. 

20-563. 

June    3, 

145,                        20-45s. 

" 

"      4> 

124,                        20-498. 

20-538. 

Means        9m.  20  -49s. 

9m.  20-51s. 

SECOND    SERIES. 


Number  of  signals. 

Method  A. 

Method  B. 

June  12, 

132, 

9m.  20-778. 

9m.  20-763 

"    13, 

132, 

20-793. 

20-77& 

"    17, 

140, 

20-77s. 

20-75s. 

«    18, 

137, 

20-693. 

20-733. 

"    20, 

148, 

20-743. 

20-75s. 

"     21, 

155, 

20-79s. 

20-74s. 

"     24, 

151, 

20-843. 

20-843. 

Means 

9m.  20-773. 

9m.  20-768. 

Concluded  longitude 

9m.  20-63s. 

9m.  20'63s. 

In  order  to  refer  the  position  of  the  observatory  of 
Greenwich  to  the  ancient  meridian  of  France,  we  must 
subtract  from  the  preceding  result  0*12s.  which  represents 


356  HISTORY  OF  ASTRONOMY. 

the  distance  between  this  meridian  and  the  present  posi- 
tion of  the  transit  instrument  of  the  Paris  observatory. 
"We  thus  have  for  the  final  result  9m.  20'51s. 

The  difference  of  longitude  between  Greenwich  and 
Paris  has  been  heretofore  determined  with  all  the 
accuracy  which  science  could  supply;  by  eclipses  of 
the  sun;  by  occultations  of  stars;  by  explosions  of 
rockets ;  by  geodetic  triangulation ;  and  by  the  trans- 
portation of  chronometers. 

The  first  important  measure  was  made  in  1790,  by  a 
triangulation  conducted  by  General  Eoy  for  England, 
and  by  MM.  Cassini,  Mechain,  and  Legendre  for  France. 
This  measurement  gave  the  difference  of  longitude 
9m.  18-8s. 

The  second  geodetic  measurement  was  made  in  1821, 
2  and  3,  by  Captains  Kater  and  Colby  for  England,  and 
by  French  astronomers  from  Calais  to  Paris.  The  result 
of  this  measurement  was  9m.  21'18s. 

In  1825  the  difference  of  longitude  was  determined  by 
fire  signals.  The  operations  were  conducted  by  Messrs. 
Herschel  and  Sabine  for  England,  and  MM.  Bonne  and 
Largeteau  for  France.  The  result  of  this  trial  was 
9m.  2146s. 

In  1838,  Mr.  Dent,  of  London,  transported  twelve  of 
his  chronometers  from  Greenwich  to  Paris,  and  returned 
them  from  Paris  to  Greenwich,  having  compared  them 
each  time  with  the  clocks  at  the  two  observatories.  The 
mean  of  the  results  furnished  by  these  chronometers  was 
9m.  22*ls.  in  going,  and  9m.  20'5s.  in  returning. 


APPLICATION  OP  THE  ELECTRIC  TELEGRAPH.       357 

The  difference  of  longitude  between  Greenwich  and 
Paris  for  nearly  thirty  years  had  been  assumed  to  be 
9m.  21s.5 ;  and  this  result  is  now  concluded  to  have  been 
too  great  by  an  entire  second  of  time. 

The  time  occupied  in  the  transmission  of  the  electric 
current  was  found  to  be  Os.086  at  Greenwich,  and  Os.079 
at  Paris,  the  distance  being  about  300  miles. 

DETERMINATION    OP    THE  VELOCITY  OP    THE    ELECTRIC 
CURRENT. 

The  experiments  of  January  23d,  1849,  between  Cam- 
bridge, New  York,  Philadelphia,  and  Washington, 
afforded  an  approximate  determination  of  the  velocity 
of  the  electric  fluid.  If  the  fluid  requires  no  time  for 
its  transmission,  then  the  star  signals  given  at  either 
station  ought  to  be  similarly  printed  at  all  the  stations  ; 
and  the  fraction  of  a  second  registered  upon  any  one 
scale  should  be  identically  the  same  as  upon  every  other. 
But  if  the  fluid  requires  time  for  its  transmission,  these 
fractions  will  be  different.  Suppose  the  clock  to  be  at 
"Washington ;  that  an  arbitrary  signal  is  made  at  Cam- 
bridge ;  and  that  the  time  required  for  the  transmission 
of  a  signal  between  the  two  places  is  the  thirtieth  of  a 
second.  Then  the  clock  pause  will  be  registered  at  Cam- 
bridge -f-yth  of  a  second  after  it  took  place  and  was  re- 
corded at  Washington,  and  the  arbitrary  signal  pause 
will  be  recorded  at  Cambridge  as  soon  as  it  is  made,  or 
s^-th  of  a  second  before  it  reaches  Washington.  We 
shall  thus  have  the  interval  between  the  signal  pause 


358  HISTORY    OF  ASTRONOMY. 

and  the  preceding  clock  pause,  longer  at  Washington 
than  at  Cambridge,  and  the  excess  on  the  Washington 
register  will  measure  twice  the  time  consumed  in  the 
transmission  of  the  signals  between  the  two  stations. 

Thus,  in  the  following  figure,  let  the  upper  line  rep- 
resent a  portion  of  the  Washington  time  scale,  corre- 
sponding to  15,  16,  etc.,  seconds,  and  the  lower  line  the 

Washington,   _J5 « * J7 18 

Cambridge,' .g_  _  -^ fl ^- 

same  for  Cambridge,  each  division  being  a  little  later 
than  the  corresponding  one  for  Washington.  Then  if 
an  arbitrary  signal  is  made  at  Cambridge  between  16  and 
17  seconds,  and  printed  at  A,  the  record  on  the  Wash- 
ington scale  will  be  at  B,  and  the  interval  from  16  to  B 
will  exceed  that  from  16  to  A  by  twice  the  time  con- 
sumed in  the  transmission  of  the  signals  from  Cambridge 
to  Washington. 

In  the  observations  of  January,  1849,  Professor 
Walker  detected  a  difference  in  the  registers  of  the  papers 
at  the  several  stations,  and  it  indicated  a  velocity  of  the 
electric  wave  of  18,800  miles  per  second.* 

On  the  31st  of  October,  1849,  similar  experiments 
were  repeated  between  Washington  and  Cincinnati,  in- 
dicating a  velocity  of  only  16,000  miles  per  second.f 

Dr.  B.  A.  Gould  has  discussed  the  same  experiments, 
and  has  deduced  from  the  observations  of  January  23d  a 

*  Proceedings  Am.  Phil.  Soc.,  vol.  V.,  p.  76. 
f  Astronomical  Journal,  vol.  I.,  p.  55. 


APPLICATION  OF  THE   ELECTRIC  TELEGRAPH.      359 

velocity  of  18,000  miles  per  second,  and  from  the  ex- 
periments of  October  31st  a  velocity  of  18,330  miles  per 
second.* 

On  the  12th  of  November,  1849,  Professor  Mitchell 
performed  a  series  of  experiments  on  the  line  between 
Pittsburg  and  Cincinnati,  the  circuit  being  formed  by  a 
wire  from  Cincinnati  to  Pittsburg,  and  a  second  wire  from 
Pittsburg  to  Cincinnati,  constituting  a  length  of  607 
miles.  The  wave  time  deduced  from  these  experiments 
was  Os.02128,  corresponding  to  a  velocity  of  28,524  miles 
per  second,  f 

The  importance  of  an  accurate  determination  of  the 
velocity  with  which  signals  travel  along  the  wires  of  the 
electric  telegraph,  induced  the  superintendent  of  the  Coast 
Survey  to  undertake  a  very  extensive  series  of  experi- 
ments for  this  purpose.  On  the  night  of  February  4th, 
1850,  the  telegraph  lines  from  "Washington  to  Pittsburg, 
from  Pittsburg  to  Louisville,  and  from  Louisville  to  St. 
Louis  were  all  united,  so  that  signals  were  transmitted 
directly  from  "Washington  to  St.  Louis,  and  recorded  on 
the  registers  of  the  four  telegraph  offices.  The  length 
of  the  wire  constituting  the  telegraph  line  was  1049 
miles,  and  the  shortest  distance  between  the  extreme 
stations  through  the  ground  was  742  miles.  The  tem- 
perature was  at  zero  of  Fahrenheit  from  Pittsburg  to 
St.  Louis,  and  at  eight  degrees  at  "Washington.  The 
insulation  was  so  perfect,  that  each  station  could  receive 

*  Proceedings  Am.  Assoc,  at  New  Haven,  p.  97. 
f  Astronomical  Journal,  vol.  L,  p.  16. 


360  HISTORY  OF  ASTRONOMY. 

the  writing  of  all,  without  change  of  adjustment.  A 
clock  in  Washington,  prepared  by  Mr.  Saxton,  graduated 
the  time  scales  on  the  Morse  registering  fillets  at  all  the 
stations,  and  arbitrary  signals  were  given  at  one  station, 
and  received  at  all  the  others.  Thus  Pittsburg,  Cin- 
cinnati, Louisville  and  St.  Louis,  were  successively,  for  a 
period  of  ten  minutes,  made  the  stations  for  arbitrary 
signals,  which  were  printed  on  all  the  registers  every 
three  seconds.  These  observations  have  been  carefully 
analyzed  by  Mr.  S.  C.  Walker,  by  Dr.  B.  A.  Gould,  and 
by  Mr.  K.  Kullman,  of  the  Bavarian  engineers.  Mr. 
Walker's  final  conclusion  is,  that  the  velocity  of  the 
galvanic  wave  in  the  iron  wires  of  the  telegraph  lines  is 
15,400  miles  per  second;  and  that  the  velocity  of  the 
wave  in  the.  ground  is  not  more  than  two  thirds  of  the 
velocity  in  the  iron  wires.*  Dr.  Gould  obtained  as 
the  most  probable  result,  a  velocity  of  14,900  miles  per 
second  through  iron  wire,  and  he  concluded  that  the 
signals  were  in  no  case  transmitted  through  the 
ground. f  Mr.  Kullman  obtained  a  mean  result  of 
13,000  miles  per  second  in  iron  wire,  and  9,740  in  the 
ground.^ 

From  the  experiments  of  February  5,  1850,  between 
Washington  and  Charleston,  Dr.  Gould  deduced  the 
velocity  of  the  electric  current  equal  to  16,856  miles 
per  second.§ 

*  Coast  Survey  Report  for  1850,  p.  87. 

f  Proceedings  Am.  Asso.  at  New  Haven,  p.  92. 

\  Ibid.,  p.  401.  §  Ibid.,  p.  97. 


APPLICATION  OF  THE  ELECTRIC  TELEGRAPH.       361 

On  the  8th  of  July,  1850,  Mr.  Walker  tried  a  variety 
of  experiments,  for  the  purpose  of  testing,  by  means  of 
the  chemical  telegraph,  the  velocity  of  propagation  of 
the  electric  current  indicated  by  the  Morse  telegraph  lines. 
These  experiments  were  performed  on  the  line  from 
Boston  to  New  York,  on  a  circuit  of  407  miles  in  length, 
220  of  which  were  of  iron  wire  in  the  air,  and  187 
were  through  the  ground.  The  marks  were  recorded  on 
paper,  previously  moistened  with  a  solution  of  ferro- 
cyanate  of  potassa.  As  there  was  no  astronomical  clock 
in  connection  with  the  line,  Mr.  Walker  tapped  at  in- 
tervals of  two  seconds  on  the  make-circuit  key,  and  thus 
graduated  the  chemical  disc  of  paper  at  Boston  and  New 
York.  The  operator  at  the  New  York  office  imprinted 
in  every  third  interval,  between  the  marks  of  the  grad- 
uated scale,  three  short  marks,  which  were  also  recorded 
at  both  stations.  These  experiments,  63  in  number, 
indicated  a  difference  of  the  New  York  marks  on  the 
Boston  time-scale,  of  about  one  second  for  every  12,000 
miles.* 

The  experiments  made  in  July  and  August,  1852,  be- 
tween Washington  and  Petersburg,  Ya.,  indicated  a 
velocity  of  the  electric  current  equal  to  9,800  miles  per 
second.f 

Numerous  experiments  have  been  made  in  France  by 
MM.  Fiseau  and  Gounelle  in  1850,  and  by  MM.  Bur- 

*  Astronomical  Journal,  vol.  I.,  p.  108. 
f  Coast  Survey  Report  for  1852,  p.  26. 

16 


362  HISTORY  OF  ASTBONOMY. 

nouf  and  Guillemin  in  1854,  to  determine  the  velocity 
of  the  electric  current.  The  following  is  the  principle 
upon  which  these  experiments  are  founded.  Conceive  an 
insulated  metallic  wire,  a  hundred  miles  or  more  in 
length,  the  two  extremities  of  which  are  brought  close 
together.  Near  one  extremity  of  the  wire,  but  not  in 
contact  with  it,  is  one  of  the  poles  of  a  battery,  of  which 
the  other  communicates  with  the  ground.  Near  the  other 
extremity  of  the  wire,  but  not  in  contact  with  it,  is  the 
wire  of  a  galvanometer,  of  which  the  other  end  com- 
municates with  the  earth.  If  at  the  same  instant  we 
touch  one  end  of  the  wire  to  the  battery  and  the  other 
to  the  galvanometer,  the  current  runs  through  the 
wire,  reaches  the  galvanometer,  and  deflects  the  needle. 
But  the  current  requires  a  certain  time  to  traverse  the 
wire.  If  the  contacts  continue  sufficiently  long,  the  cur- 
rent will  reach  the  galvanometer,  and  deflect  the  needle. 
If  the  contacts  do  not  continue  sufficiently  long,  the 
current  will  not  reach  the  galvanometer,  and  the  needle 
will  not  be  deflected.  By  gradually  diminishing  the 
time  of  contact,  we  may  determine  the  exact  interval  at 
which  the  deviation  ceases.  This  interval  is  the  time 
which  the  current  requires  to  traverse  the  wire. 

The  contacts  are  made  by  the  rapid  revolution  of  a 
wheel  whose  circumference  consists  of  narrow  strips  of 
wood  and  brass  alternately. 

MM.  Guillemin  and  Burnouf  concluded  from  their 
experiments  that  the  velocity  of  the  electric  current  in 
an  iron  wire  one  sixth  of  an  inch  in  diameter,  was 


APPLICATION  OF  THE  ELECTKIC  TELEGRAPH.    363 

108,900  miles  per  second.*  MM.  Fiseau  and  Gounelle 
deduced  a  velocity  of  112,680  miles  per  second  in  copper 
wire  one  tenth  of  an  inch  in  diameter,  and  62,600  miles 
in  iron  wire  one  sixth  of  an  inch  in  diameter.f 

All  these  results  differ  materially  from  that  obtained  in 
1836  by  Professor  Wheatstone,  who  determined  the 
velocity  of  frictional  electricity  to  be  288,000  miles  per 
second.  Professor  Faraday  is  of  opinion  that  the  veloc- 
ity of  discharge  through  the  same  wire  must  vary  with 
the  tension  or  intensity  of  the  first  urging  force  ;  and  on 
account  of  the  lateral  induction  of  the  current,  he  con- 
siders that  the  velocity  must  be  different  if  the  wires  be 
turned  round  a  frame  in  small  space,  or  be  spread  through 
the  air  through  a  large  space,  or  adhere  to  walls,  or  be 
laid  upon  the  ground. 

The  telegraph  wires  from  London  to  Manchester  are 
covered  with  gutta-percha  inclosed  in  metallic  tubes,  and 
buried  in  the  earth ;  and  when  they  are  all  connected  so 
as  to  make  one  series,  form  a  length  of  over  1500  miles. 
Professor  Faraday  placed  one  galvanometer  at  the  be- 
ginning of  the  wire ;  a  second  galvanometer  in  the 
middle ;  and  a  third  at  the  end ;  the  three  galvanometers 
being  side  by  side  in  the  same  room,  and  the  third  per- 
fectly  connected  with  the  earth.  On  bringing  the  pole 
of  a  battery  into  contact  with  the  wire  through  the  gal- 
vanometers, the  first  galvanometer  was  instantly  affected; 
after  about  a  second  the  next  was  affected;  and  it  re- 
quired two  seconds  for  the  electric  stream  to  reach  the 

*  Comptes  Kendus,  Aug.  14,  1854.  f  Ibid.,  April  15,  1850. 


364  HISTORY  OF  ASTRONOMY. 

last  galvanometer.  Again,  all  the  instruments  being  de- 
flected, when  the  battery  was  cut  off,  the  first  galvanom- 
eter instantly  fell  to  zero ;  but  the  second  did  not  fall 
until  a  little  while  after ;  and  the  third  only  after  a  still 
longer  interval — a  current  flowing  on  to  the  end  of 
the  wire,  while  there  was  none  flowing  in  at  the  be- 
ginning. 

DIFFERENCES  OF  DECLINATION  RECORDED  BY  ELECTRO- 
MAGNETISM. 

Differences  of  decimation  may  be  recorded  by  means  of 
electro-magnetism.  This  is  accomplished  by  inserting  in 
the  focus  of  the  meridional  telescope  two  systems  of 
spider  lines,  one  vertical,  and  the  other  inclined  at  an 
angle  of  45°.  Let  A  B  represent  the  horizontal  wire  of 
the  transit  instrument,  D  E  the 
middle  vertical  wire,  and  F  Gr  a 
wire  inclined  to  the  latter  at  an 
angle  of  45°.  Let  the  telescope 
be  pointed  upon  a  star  as  it  ap- 
proaches the  meridian,  and  let  it 
be  bisected  by  the  wire  A  B,  while 
the  time  of  passing  the  vertical  wire  D  E  is  recorded. 
Let  the  telescope  remain  firmly  fixed  in  its  position,  and 
suppose  a  second  star  enters  the  field  at  H  and  traverses 
the  path  H  L.  Let  the  instant  of  passing  F  Gr  at  I,  and 
D  E  at  E  be  recorded.  Then  if  the  angle  D  0  F  is  45°, 
C  K  (which  is  the  difference  of  declination  of  the  two 
stars)  will  be  equal  to  K  I.  The  line  K I  is  measured  by 


APPLICATION   OF  THE   ELECTRIC  TELEGRAPH.       365 

the  time  required  for  the  star  to  describe  this  portion  of 
its  path ;  and  the  observed  time  is  easily  converted  into 
arc  of  a  great  circle.  If  a  third  star  enters  the  field  at 
M,  and  crosses  the  wire  D  E  at  N,  and  F  G  at  O,  then 
C  N  is  the  difference  of  declination  of  the  first  and  third 
stars ;  and  in  the  same  manner,  by  observing  the  transits 
of  any  number  of  stars  over  the  wires  D  E  and  F  G,  in 
the  same  position  of  the  telescope,  we  shall  obtain  their 
differences  of  declination  as  well  as  of  right  ascension. 
In  order  to  diminish  the  errors  of  observation,  we  intro- 
duce a  large  number  of  inclined  wires,  at  intervals  of  two 
or  three  seconds  from  each  other,  as  well  as  a  large  num- 
ber of  vertical  wires ;  and  the  times  of  transit  over  each 
system  of  wires  are  recorded  by  electro-magnetism. 

This  method  is  well  adapted  to  the  construction  of  a 
catalogue  of  stars,  where  it  is  proposed  to  record  the 
position  of  every  star  within  the  range  of  the  telescope. 
For  this  purpose  the  telescope  is  firmly  clamped,  and  re- 
mains fixed  in  its  position  during  the  observations  of  an 
entire  evening  or  night,  while  the  observer,  sitting  with  his 
eye  at  the  telescope,  has  but  to  press  his  finger  upon  a  key 
at  the  instant  a  star  is  seen  to  pass  each  wire  of  the  two  sys- 
tems already  mentioned.  This  mode  of  observation  has  been 
practiced  at  the  Washington  observatory  since  1849.  The 
wires  for  right  ascension  are  35  in  number,  and  are  divided 
into  groups  or  fascicles  of  five  each,  the  interval  between 
two  wires  being  from  two  to  three  seconds.  To  complete 
a  set  of  observations  on  any  one  fascicle  requires  only 
from  eight  to  ten  seconds.  The  wires  for  differences  of 


366 


HISTORY  OF  ASTRONOMY. 


declination  are  also  35  in  number,  and  are  arranged 
in  groups  of  five  each.  In  order  to  prevent  any  con- 
fusion between  observations 
for  right  ascension  and  those 
for  declination,  the  rule  is-, 
to  observe  for  right  ascen- 
sion on  one  fascicle  of  wires 
first ;  then  by  a  telegraphic 
symbol,  to  denote  the  mag- 
nitude of  the  star ;  and  after- 
ward to  observe  it  on  a  fas- 
cicle of  inclined  wires  for 
declination.  The  several  fascicles  are  distinguished  from 
each  other  by  the  inequalities  of  the  intervals. 

Professor  0.  M.  Mitchell  has  invented  a  different 
method  of  registering  the  declinations  of  the  heavenly 
bodies  by  means  of  the  electric  circuit,  dispensing  entirely 
with  the  use  of  a  graduated  circle.  For  this  purpose,  he 
attaches  firmly  to  the  axis  of  his  transit  instrument  by  a 
strong  clamp  collar,  a  light  bar,  about  six  feet  in  length. 
To  the  upper  part  of  this  arm  an  electro-magnet  is  fixed, 
which  operates  a  double  lever  armed  with  a  steel  record- 
ing pen.  To  receive  the  record,  a  metallic  plate  is  placed 
vertically  on  the  face  of  the  transit  pier,  moving  in  ways 
parallel  to  the  circles  described  by  the  recording  pen. 
To  use  this  instrument  for  record,  the  observer  sets  for 
his  standard  star ;  the  arm  is  then  brought  to  the  vertical 
and  clamped.  The  instrument  is  then  clamped,  and  a 
tangent  screw  gives  to  the  observer  his  slow  motion  for 


APPLICATION  OF   THE  ELECTPJC  TELEGRAPH.       367 

bringing  the  star  to  the  declination  wires.  When  the  star 
is  bisected,  the  observer  strikes  the  key  with  his  finger,  the 
circuit  is  formed,  the  electro-magnet  brings  the  pen  in 
contact  with  the  record  plate ;  and  while  in  contact,  the 
plate  descends  in  its  ways,  and  a  zero  line  is  described  on 
the  plate,  from  which  all  differences  of  declination  are 
afterward  read.  Professor  Mitchell  uses  three  declination 
wires,  and  there  are  three  zero  lines  obtained  from  the 
standard  star.  When  the  difference  of  declination  of  one 
star  has  been  recorded,  the  plate  moves  upward  about 
the  tenth  of  an  inch,  and  is  ready  for  the  next  record. 

To  read  the  record  of  declination,  the  plate  is  laid  on 
a  carriage  and  leveled  by  four  screws :  a  movable  arc, 
divided  into  equal  parts,  whose  values  have  been  abso- 
lutely determined  and  tabulated,  is  adjusted  so  that  its 
zero  coincides  with  the  zero  line  of  the  record.  It  then 
glides  on  its  ways,  parallel  to  and  just  above  the  record 
plate.  A  micrometer  screw,  and  microscope,  with  a 
spider's  web,  read  the  fractions  of  the  equal  parts  into 
which  the  arc  is  divided,  with  great  facility  and  with 
great  accuracy. 


SECTION  7. 

ASTRONOMICAL  PUBLICATIONS. 

AMONG  astronomical  publications  in  this  country,  the 
translation  of  La  Place's  Mecanique  Celeste,  by  Bow- 
ditch,  deservedly  holds  the  first  rank.  Although  in 
name  merely  a  translation  of  a  foreign  book,  with  a  com- 
mentary, it  has  many  claims  io  the  character  of  an 
original  work. 

The  observations  made  by  Lieutenant  Gilliss  at  "Wash- 
ington from  1838  to  1842,  have  been  published  by  order 
of  Congress,  and  form  an  octavo  volume  of  672  pages. 
Three  volumes  of  observations,  made  at  the  Naval  ob- 
servatory at  Washington,  have  been  published.  The 
observations  for  1845  constitute  a  quarto  volume  of  550 
pages,  with  13  plates ;  the  observations  for  1846  consti- 
tute a  quarto  of  676  pages;  and  the  observations  for 
1847  constitute  a  volume  of  480  pages,  accompanied  by 
44  plates,  showing  a  series  of  observations  of  solar  spots 
by  Professor  Sestini,  made  at  Georgetown  observatory. 

In  1852  was  published  No.  1  of  the  "  Annals  of  the 
Georgetown  Observatory,"  being  a  quarto  volume  of 
216  pages,  chiefly  occupied  with  a  description  of  the 
building  and  instruments. 


ASTRONOMICAL  PUBLICATIONS.  369 

In  1855  was  published  Yol.  L,  Part  II,  of  the  "An- 
nals of  Harvard  College  Observatory,"  being  a  quarto 
volume  of  416  pages,  containing  a  catalogue  of  5,500 
stars  situated  between  the  equator  and  0°  20'  north  dec- 
lination. 

With  the  preceding  exceptions,  the  American  contri- 
butions to  astronomical  science  are  to  be  found  in 
periodicals  and  the  transactions  of  scientific  societies. 

The  Transactions  of  the  Eoyal  Society  of  London 
contain  some  observations  by  American  astronomers 
before  the  Eevolution.  The  Transactions  of  the  Ameri- 
can Philosophical  Society  contain  valuable  papers  from 
Kittenhouse,  Ewing,  Smith,  Ellicott,  Dunbar,  Lambert, 
Adrain,  Hassler,  Gummere,  Talcott,  Courtenay,  Loomis, 
Mason,  Nicollet,  "Walker,  Kendall,  Bartlett,  Gilliss,  and 
several  others.-  Among  the  subjects  of  these  communi- 
cations may  be  enumerated  the  transit  of  Venus  in  1769 ; 
the  transit  of  Mercury  in  1769 ;  the  comets  of  1770, 
1807,  1842,  1843,  and  1844 ;  the  solar  eclipses  of  1791, 
1803,  1806,  1831,  1834,  1836,  and  1838 ;  numerous  oc- 
cultations  of  stars  ;  moon  culminations ;  observations  of 
nebulae ;  observations  and  computations  for  the  latitude 
and  longitude  of  numerous  places  in  this  country. 

The  Memoirs  and  Proceedings  of  the  American 
Academy  contain  important  papers  from  Willard,  Wil- 
liams, Winthrop,  Webber,  Dean,  Bowditch,  Fisher, 
Paine,  W.  C.  Bond,  G.  P.  Bond,  and  Graham.  Among 
the  subjects  of  these  papers  may  be  enumerated  observa- 
tions of  the  transits  of  Mercury  in  1782,  1789,  and  1845 ; 

16* 


370  HISTORY  OF  ASTRONOMY. 

the  comets  of  1807,  1811,  1819,  1845,  1846,  and  1847  ; 
the  solar  eclipses  of  1780,  1781,  1782,  1791,  1806,  1811, 
1845,  and  1846 ;  various  occupations  of  stars  ;  observa- 
tions of  nebulas ;  and  observations  and  computations  for 
the  latitude  and  longitude  of  various  places  in  the 
United  States. 

The  Memoirs  of  the  Connecticut  Academy  contain 
observations  of  the  comets  of  1807  and  1811,  by  Mans- 
field and  Day,  and  the  calculation  of  the  longitude  of 
Yale  Colleger 

The  Transactions  of  the  Albany  Institute  contain  a 
notice  of  the  solar  eclipse  of  1806,  by  Simeon  De  Witt, 
and  observations  of  the  solar  eclipses  of  1831  and  1832, 
by  Professor  S.  Alexander. 

The  American  Journal  of  Science  contains  some 
original  observations  of  comets  and  eclipses,  and  has 
been  the  vehicle  for  the  diffusion  of  much  valuable  in- 
formation respecting  subjects  of  passing  interest. 

The  American  Almanac,  which  has  been  published 
regularly  since  1830,  has  given  each  year  very  full  com- 
putations of  all  visible  eclipses,  and  the  elements  for  the 
calculation  of  occultations  of  stars  by  the  moon.  These 
I  computations  were  made  by  Mr.  E.  T.  Paine  until  the 
1  year  1841,  and  since  that  time  by  Professor  Pierce  and 
\Mr.  G.  P.  Bond. 

The  United  States  Almanac,  which  only  continued  for 
three  years,  gave,  in  addition  to  the  usual  astronomical 
articles,  a  great  variety  of  tables  useful  to  computers. 

The  computation  of  the  occultations  of  all  stars  down 


ASTRONOMICAL  PUBLICATIONS.  371 

to  the  sixth  magnitude,  for  nearly  twenty  years,  has  been 
made  by  Messrs.  Walker,  Downes  and  Paine.  Mr. 
Downes'  computations  for  the  years  1848,  1849,  1850 
and  1851,  have  been  published  by  the  Smithsonian 
Institution.  They  contain  the  times  of  all  the  occulta- 
tions  visible  at  "Washington,  and  elements  for  facilitating 
a  similar  computation  for  any  part  of  North  America. 

During  the  session  of  1849,  Congress  made  an  ap- 
propriation of  $6,000  for  the  commencement  of  an 
American  Nautical  Almanac.  Lieutenant  (now  Com- 
mander) Charles  H.  Davis,  of  the  United  States  Navy, 
was  appointed  superintendent,  and  the  preparation  of 
different  parts  of  the  work  was  assigned  to  a  corps  of 
computers.  Lieutenant  Davis  secured  the  valuable 
services  of  Professor  Peirce  as  consulting  astronomer; 
the  theoretical  part  of  the  work  was  placed  under  his 
direction;  and  most  of  the  calculations  pass  under  his 
final  revision. 

The  first  volume  was  published  in  1852,  being  the 
almanac  for  1855,  consisting  of  552  octavo  pages.  The 
first  part  of  the  work  is  appropriated  to  nautical  purposes, 
and  is  calculated  for  the  meridian  of  Greenwich.  The 
second  part  is  designed  for  the  promotion  of  astronomi- 
cal science,  and  is  adapted  to  the  meridian  of  Wash- 
ington. The  nautical  part  consists  of  an  ephemeris  of 
the  sun  and  moon,  and  of  the  planets  Venus,  Mars,  Ju- 
piter and  Saturn,  together  with  tables  of  lunar  distances. 
The  ephemeris  of  the  moon  is  calculated  from  new  tables 
founded  on  Plana's  theory.  The  ephemeris  of  Mercury 


372  HISTORY  OF  ASTRONOMY. 

is  derived  from  the  theory  given  by  Le  Verrier;  the 
ephemeris  of  Venus  is  founded  on  Lindenau's  tables,  with 
corrections  from  the  labors  of  Breen,  Airy  and  Le 
Verrier.  The  ephemeris  of  Uranus  is  calculated  'from 
Bouvard's  ellipse,  combined  with  Le  Vender's  perturba- 
tions by  Jupiter  and  Saturn,  and  Peirce's  perturbations 
due  to  Neptune.  The  ephemeris  of  Neptune  is  founded 
on  "Walker's  orbit  and  Peirce's  perturbations. 

The  Almanac  for  1856  was  published  in  1853.  It 
constitutes  a  volume  of  574  pages,  and  is  prepared  upon 
nearly  the  same  plan  as  the  preceding  volume.  The 
Almanac  for  1857  was  published  in  1854 ;  and  that  for 
1858  was  published  in  1855. 

The  first  periodical  undertaken  in  this  country  de- 
voted exclusively  to  astronomy,  was  the  Sidereal  Mes- 
senger, edited  by  Professor  Mitchell.  This  was  designed 
to  exhibit  in  a  popular  form  the  recent  discoveries  in 
astronomy,  and  by  this  means  to  cultivate  a  more  general 
taste  for  astronomical  science.  The  work  was  com- 
menced in  July,  1846,  and  continued  for  a  little  over 
two  years,  .when  it  was  abandoned  for  want  of  patronage. 

At  the  meeting  of  the  American  Association  for  the 
Advancement  of  Science  at  Cambridge  in  August,  1849, 
Professor  J.  S.  Hubbard  presented  a  paper  on  the  estab- 
lishment of  an  astronomical  journal  in  the  United  States, 
and  the  subject  was  referred  to  a  select  committee.  The 
proposition  was  generally  approved,  and  the  first  num- 
ber of  the  "  Astronomical  Journal"  was  issued  in  No- 
vember, 1849,  under  the  editorship  of  Dr.  B.  A.  Gould. 


ASTKONOMICAL  PUBLICATIONS.  373 

This  journal  is  devoted  exclusively  to  the  publication 
of  original  researches  and  observations  in  astronomy, 
geology  and  kindred  branches.  It  is  conducted  upon  the 
model  of  the  Astronomische  Nachrichten  of  Professor  Schu- 
macher, and  the  numbers  appear  at  irregular  intervals, 
as  matter  accumulates,  or  important  information  is  re- 
ceived. A  volume  consists  of  twenty-four  numbers, 
each  containing  eight  octavo  pages.  Vol.  I.  was  com- 
pleted in  April,  1851.  Yol.  IT.  was  completed  in  Sep- 
tember 1852.  Yol.  EL  in  June  1854 ;  and  No.  22  of' 
Yol.  IY.  was  published  in  June,  1856.  The  numbers  have 
accordingly  averaged  a  little  more  than  one  .per  month. 

This  journal  has  attained  a  high  reputation,  and  has 
imparted  a  fresh  impulse  to  the  cause  of  science  in  the 
United  States.  It  contains  numerous  observations  of 
newly  discovered  comets  and  planets  made  in  Europe  as 
well  as  the  United  States,  together  with  remarks  respect- 
ing the  orbits  of  these  bodies  and  various  questions  in 
astronomy  and  the  pure  mathematics.  Notice  of  the  first 
discovery  of  a  comet  or  a  planet  is  immediately  an- 
nounced by  a  special  circular,  so  that  the. attention  of 
observers  throughout  the  country  is  immediately  directed 
to  these  bodies. 

The  tables  from  which  the  lunar  ephemeris  in  the 
Nautical  Almanac  was  computed,  have  been  published  in 
a  quarto  volume  of  326  pages.  These  tables  were  con- 
structed from  Plana's  theory,  with  Airy's  and  Long- 
streth's  corrections ;  with  Hansen's  two  inequalities  of  long 
period  arising  from  the  action  of  Venus,  an#  Hansen's 


374  HISTORY  OF  ASTRONOMY. 

values  of  the  secular  variations  of  the  mean  motion 
and  of  the  motion  of  the  perigee  ;  and  they  are  arranged 
in  a  form  designed  by  Professor  Peirce. 

Mayer's  Lunar  Tables,  which  were  published  in  1753, 
represented  the  moon's  place  with  greater  accuracy  than 
any  which  had  hitherto  been  constructed.  The  number 
of  arguments  used  in  calculating  the  moon's  longitude 
was  fourteen.  These  tables  received  the  approbation  of 
the  British  Board  of  Longitude,  and  the  widow  of  Mayer 
received  on  account  of  them  a  considerable  sum  of 
money  from  the  British  government. 

In  1780  were  published  Mason's  Tables  of  the  Moon. 
In  their  construction  and  arrangement  they  resembled 
Mayer's  tables,  but  the  number  of  arguments  employed  in 
calculating  the  moon's  longitude  amounted  to  twenty-two. 

In  1806  Burg's  Lunar  Tables  were  published  under  the 
auspices  of  the  French  Bureau  des  Longitudes.  The 
number  of  arguments  employed  in  the  calculation  of  the 
moon's  longitude  was  twenty-eight. 

In  1812,  Burckhardt's  Lunar  Tables  were  published. 
The  number  of  arguments  in  the  moon's  longitude  was 
thirty-six. 

In  1824,  appeared  Damoiseau's  Tables  of  the  Moon, 
founded  solely  on  his  own  theoretical  researches.  The 
number  of  arguments  in  the  moon's  longitude  is  forty- 
seven. 

The  American  Lunar  Tables  are  constructed  upon  a 
plan  recommended  by  Carlini.  The  number  of  argu- 
ments for*the  moon's  longitude  is  seventy-nine. 


SECTION  VI. 

THE    MANUFACTURE    OP   TELESCOPES    IN    THE    UNITED 
STATES. 

VARIOUS  attempts  have  been  made  in  this  country  to 
manufacture  both  reflecting  and  refracting  telescopes.  I 
shall  speak  of  each  of  them  in  succession. 

REFLECTING-   TELESCOPES. 

A  great  many  reflecting  telescopes  have  been  con- 
structed by  amateur  astronomers  in  different  parts  of  the 
country ;  but,  for  the  most  part,  these  attempts  have 
been  but  moderately  successful,  and  have  contributed 
but  little,  if  any  thing,  to  the  progress  of  science.  The 
most  important  exception  to  this  remark  was  in  the  case 
of  a  telescope  manufactured  in  1838,  by  Messrs.  Smith, 
Mason  and  Bradley,  the  two  former  gentlemen  being  at 
that  time  students  of  Yale  College.  This  telescope  had 
an  aperture  of  twelve  inches,  and  a  focal  length  of 
fourteen  feet.  The  mirror  was  cast,  ground,  and  polished 
by  their  own  hands.  Stars  of  less  than  one  second's 
distance,  were  separated  by  this  instrument;  the  faint 
star,  " debilissima,"  near  e  Lyrae,  was  easily  shown; 
and  the  nebula  in  Hercules,  between  t]  and  £,  was  re- 


376  HISTOEY  OF  ASTEONOMY. 

solved  into  an  immense  number  of  small  stars.  With 
this  instrument,  Mr.  Mason  made  some  very  accurate 
observations  of  three  nebulas,  of  which  an  account  is 
given  in  the  Transactions  of  the  American  Philosoph- 
ical Society.  This  paper  affords  but  a  foretaste  of 
what  might  have  been  anticipated  from  the  talents  of 
Mr.  Mason,  had  not  his  course  been  arrested  by  his 
premature  death,  which  occurred  Dec.  26th,  1840. 

Several  mechanics  have  undertaken  the  manufacture 
of  reflecting  telescopes  for  sale,  but  the  only  one  who 
has  pursued  this  business  to  any  great  extent  is  Mr. 
Amasa  Holcomb,  of  Southwick,  Massachusetts.  Mr. 
Holcomb  first  attempted  the  grinding  and  polishing 
lenses  about  the  year  1826.  He  then  proceeded  to  the 
manufacture  of  refracting  telescopes,  but  being  dis- 
couraged by  the  difficulty  of  obtaining  suitable  glass, 
he  turned  his  attention  to  reflectors.  In  this  he  sue?- 
ceeded  remarkably  Well,  and  now  his  telescopes  are 
found  in  almost  every  State  of  the  Union,  and  some 
have  been  ordered  for  foreign  countries.  Mr.  Holcomb 
now  manufactures  four  sizes  of  instruments. 

The  first  size  is  14  feet  long  and  10  inches  aperture, 
with  six  eye-pieces,  magnifying  from  100  to  1000 
times. 

The  second  size  is  10  feet  long  and  8  inches  aperture, 
with  six  eye-pieces,  magnifying  from  60  to  800  times. 

The  third  size  is  7j  feet  long  and  six  inches  aperture, 
with  five  eye-pieces,  magnifying  from  40  to  600  times. 

The  fourth  size  is  five  feet  long  and  four  inches  aper- 


THE  MANUFACTURE   OF  TELESCOPES.  377 

ture,  with  four  eye-pieces,  magnifying  from  40  to  300 
times. 

These  telescopes  are  of  the  Herschelian  form,  and  have 
received  medals  from  the  American  Institute  of  New 
York,  and  the  Franklin  Institute  of  Philadelphia,  after  a 
most  thorough  and  severe  examination.  With  a  tele- 
scope of  the  second  size,  the  double  stars,  51  Librae, 
and  £  Bootis,  the  components  of  which  are  distant  from 
each  other  but  little  more  than  one  second,  have  been 
easily  separated,  and  Saturn's  ring  seen  double  nearly 
throughout  its  visible  portion.  Mr.  Holcomb  has  sold 
five  telescopes  of  his  first  size,  and  as  many  of  the 
second,  with  a  much  larger  number  of  the  smaller 
sizes. 

KEFEACTING  TELESCOPES. 

The  experiments  which  have  been  made  in  this 
country  in  the  manufacture  of  refracting  telescopes,  may 
be  divided  into  two  classes  :  namely  those  which  have 
employed  American  glass,  and  those  which  have  em- 
ployed foreign  glass. 

Several  telescopes  of  small  dimensions  have  been  made 
of  American  glass,  which  have  performed  quite  satisfac- 
torily; but  the  attempts  to  make  large  telescopes  with 
American  glass,  so  far  as  the  results  have  been  laid  be- 
fore the  public,  have  invariably  proved  failures.  At 
several  establishments  in  this  country,  glass  is  manufac- 
tured which  answers  perfectly  all  the  ordinary  purposes 
of  the  arts,  and  for  transparency,  compares  well  with 


378  HISTOEY  OF  ASTRONOMY. 

foreign  glass ;  but  it  has  been  found  impossible  to  obtain 
large  discs  possessing  that  entire  homogeneity  and  free- 
dom from  veins  which  are  demanded  in  a  lens  in  order 
that  it  may  produce  a  perfect  image. 

In  the  years  1846  and  '48,  Mr.  Alvan  Clark,  of  Boston, 
made  two  telescopes  of  East  Cambridge  flint-glass,  having 
an  aperture  of  five  inches,  which  will  show  the  division 
of  the  close  pair  in  Zeta  Cancri,  and-  Zeta  Bootis,  whose 
distance  is  about  one  second.  He  has,  however,  ex- 
pressed his  determination  to  make  no  more  telescopes  of 
American  glass,  until  he  can  find  specimens  of  a  better 
quality.  It  may  be  safely  asserted,  notwithstanding  some 
pretensions  to  the  contrary,  that  no  good  telescope  of 
large  dimensions  has  yet  been  manufactured  of  American 
glass. 

Ever  since  the  invention  of  the  achromatic  telescope  by 
Dollond,  about  a  century  ago,  one  of  the  greatest  obstacles 
to  the  construction  of  large  telescopes,  has  been  the  diffi- 
culty of  obtaining  large  discs  of  glass  of  perfectly  uniform 
density  and  free  from  veins.  The  chief  difficulty  seems 
to  arise  from  the  difference  in  the  specific  gravity  of  the 
constituents  of  glass ;  some  melt  at  a  lower  temperature, 
and  sinking  through  the  mixture,  leave  a  streak  in  de- 
scending; some  decompose  in  a  heat  required  for  the 
fusion  of  others.  It  has  been  said  that  the  glass  em- 
ployed by  Dollond  in  the  manufacture  of  his  best  tele- 
scopes was  all  made  'at  the  same  time ;  and  the  largest 
achromatic  object  glasses  constructed  in  England,  until 
recently,  did  not  exceed  five  inches  in  diameter.  More 


THE  MANUFACTURE  OF  TELESCOPES.  379 

than  half  a  century  ago,  the  English  Board  of  Longitude 
offered  a  considerable  reward  for  bringing  the  art  of 
making  flint-glass  for  optical  purposes  to  the  requisite 
perfection,  but  it  led  to  no  important  discoveries.  The 
Academy  of  Sciences  at  Paris,  offered  prizes  in  vain  for 
this  object ;  and  it  remained  for  a  man,  not  distinguished 
by  education,  nor  a  glass-maker  by  trade,  M.  Guinand, 
of  Switzerland,  to  have  the  honor  of  arriving  at  the  solu- 
tion of  the  difficulty. 

Guinand  was  born  at  Brenets,  near  Neufchatel,  and 
was  a  workman  in  the  clock  and  watch  trade.  Having 
been  permitted  to  inspect  an  achromatic  telescope,  he  de- 
termined to  make  one  for  himself,  but  could  find  no  glass 
suitable  for  this  purpose  in  Switzerland.  He  obtained 
some  flint-glass  from  England,  but  this  was  not  always 
perfectly  pure.  He  melted  it  anew,  but  did  not  obtain 
satisfactory  glass.  He  then  erected  on  the  river  Doubs, 
near  Brenets,  an  establishment  in  which  he  constructed, 
with  his  own  hands,  a  very  large  furnace,  and  commenced 
the  manufacture  of  glass,  and  finally  succeeded  in  obtain- 
ing pieces  large  enough  for  telescopes.  He  visited  Paris 
in  1798,  and  exhibited  discs  of  from  four  to  six  inches  in 
diameter.  He  afterward  discovered  a  method  of  soften- 
ing pieces  of  perfectly  pure  glass,  for  the  purpose  of 
giving  them  the  form  of  a  disc.  In  the  year  1805,  Gui- 
nand was  invited  by  Eeichenbach  to  assist  him  in  his 
optical  establishment  which  he  had  founded  at  Benedict- 
burn,  about  40  miles  from  Munich.  Here  he  remained 
nine  years,  but  always  in  a  subordinate  capacity.  In 


380  HISTORY  OF  ASTRONOMY. 

1814,  lie  returned  to  Brenets,  and  established  a  separate 
manufactory,  where  he  made  telescopes,  and  furnished 
both  flint  and  crown-glass.  In  1823,  he  was  able  to  pro- 
duce a  disc  of  a  foot  and  a  half  in  diameter.  In  1824,  he 
exhibited  at  the  exposition  of  industry  at  Paris,  a  grand 
achromatic  object-glass,  which  excited  the  admiration  of 
the  king,  who  solicited  the  son  of  Guinand,  then  present, 
to  invite  his  father  to  take  up  his  residence  at  Paris. 
Unfortunately,  the  optician  was  not  in  a  condition  to 
remove.  He  died  in  1825,  at  the  advanced  age  of  nearly 
80  years. 

Another  individual  who  contributed  to  the  reputation 
of  the  establishment  of.  Keichenbach,  perhaps  even  more 
than  Gruinand,  was .  the  illustrious  Fraunhofer.  Fraun- 
hofer  was  born  at  Straubing,  in  Bavaria,  in  1787,  and  at 
twenty  years  of  age  (in  1807)  was  received  into  the  man- 
ufactory of  Eeichenbach.  He  here  exhibited  the  most 
extraordinary  talents,  and  introduced  many  improve- 
ments into  the  manufacture  of  glass,  as  well  as  in  the  art 
of  polishing  the  spherical  surfaces  of  large  object-glasses. 
His  crowning  glory  was  the  manufacture  of  a  telescope  of 
nearly  ten  inches  aperture,  which  was  purchased  for  the 
observatory  of  Dorpat,  in  Eussia. 

It  has  been  asserted  that  the  object  glass  of  the  Dorpat 
telescope  was  made  from  glass  cast  by  Guinand;  but 
this  has  been  positively  denied  by  Utschneider,  who 
states  that  the  glass  for  the  Dorpat  telescope  was  cast 
by  Fraunhofer,  after  Guinand  left  the  establishment  at 
Benedictburn ;  and  he  also  states  that  the  glass  which 


THE  MANUFACTUKE  OF  TELESCOPES.  381 

Guinand  made  was  not  equal  in  quality  to  that  which 
Fraunhofer  made  at  a  later  period.  There  can,  however, 
be  little  doubt  that  much  of  the  reputation  of  the  Munich 
telescopes  has  resulted  from  Guinand's  experiments  in 
the  manufacture  of  glass.  The  art  of  making  this  glass 
is  kept  a  secret.  Many  particulars  of  this  manufacture 
therefore  can  only  be  conjectured.  Faraday  found  the 
specific  gravity  of  Guinand's  flint-glass  to  be  about 
3*616,  and  that  its  composition  was  silica  44*3,  oxyd  of 
lead  43-05,  and  potash  11-75.  It  is  said  that  Guinand's 
original  practice  was  to  saw  the  blocks  of  glass  which  he 
obtained  at  one  casting,  into  horizontal  sections,  supposing 
that  every  part  of  the  same  horizontal  section  would  have 
the  same  density.  A  fortunate  accident  conducted  him 
to  a  better  process.  While  his  men  were  one  day  carry- 
ing a  block  of  this  glass  on  a  hand-barrow  to  a  saw  ™fl\ 
the  mass  slipped  from  its  bearers,  and  rolling  down  a 
declivity  was  broken  to  pieces.  Guinand  selected  those 
fragments  which  appeared  perfectly  homogeneous,  and 
softened  them  in  circular  molds  in  such  a  manner  that 
on  cooling,  he  obtained  discs  that  were  afterward  fit  fc 
working.  To  this  method  he  adhered,  and  contrived  a 
way  of  cleaving  his  glass  while  cooling,  so  that  the  frac- 
tures should  follow  the  most  faulty  parts.  When  flaws 
occur  in  the  large  masses,  they  are  removed  by  cleaving 
the  pieces  with  wedges,  and  then  softening  them  again  in 
molds  which  give  them  the  form  of  discs. 

It  will  be  remembered  that  glass  softens  so  as  to  be 
readily  molded  into  any  required  shape,  at  a  tempera- 


382  HISTORY  OF  ASTKONOMY. 

ture  much  below  that  of  complete  fusion ;  and  it  appears 
to  be  requisite  in  this  second  operation  of  forming  the 
glass  into  discs,  to  stop  short  of  the  melting  point.  If 
the  glass  be  completely  melted,  bubbles  of  air  rise 
through  the  glass,  and  are  found  caught  in  the  glass  after 
it  is  cooled,  diminishing  its  transparency,  and  perhaps 
causing  even  worse  defects.  Many  discs  are  spoiled  in 
this  manner.  The  advantage  of  allowing  the  glass  to 
cool  before  it  is  cast  into  discs,  is,  that  it  affords  an  op- 
portunity to  inspect  the  casting,  and  select  such  portions 
as  appear  less  faulty.  Each  fragment  is  then  put  in  a 
separate  crucible  or  mold,  having  a  diameter  such  as  it 
is  proposed  to  give  to  the  disc,  and  softened  by  heat 
until  it  accomodates  itself  perfectly  to  the  mold;  and 
some  discs  have  marks  of  having  been  pressed  down 
into  the  molds  by  a  weight  upon  the  top;  It  is  then 
annealed  by  slow  cooling  in  the  manner  of  ordinary  glass 
ware. 

After  the  death  of  M.  Guinand,  his  widow  and  one  of 
his  sons  set  up  works  in  Switzerland,  upon  the  father's 
principles,  and  were  succeeded  by  M.  Theodore  Daguet 
(of  Soleure,  near  Neuchatel),  who  sent  to  the  London 
Exhibition  of  1851,  several  discs  of  flint-glass,  the  largest 
being  15  inches  in  diameter ;  and  a  disc  of  crown-glass 
of  7  inches  diameter,  which  were  examined  and  found  to 
be  good.  M.  Daguet,  by  a  process  of  his  own,  gives  to 
flint-glass  a  degree  of  hardness  not  attained  by  any  other 
manufacturer.  His  glass,  particularly  the  flint,  is  distin- 
guished both  by  its  homogeneousness  and  its  peculiar 


THE   MANUFACTURE  OF  TELESCOPES. 


383 


property  of  resisting  all  decomposition  by  the  action  of 
air.  A  council  medal  was  awarded  to  him  at  the  London 
Exhibition. 

The  other  son  of  Guinand  was  introduced  by  M.  Lere- 
bours,  of  Paris,  to  M.  Bontemps,  who  had  devoted  much 
•attention  to  the  manufacture  of  glass  generally,  and  par- 
ticularly of  such  as  is  required  for  optical  purposes.  He 
formed  an  association  with  Bontemps,  which,  however, 
was  not  of  long  continuance.  In  1828,  they  succeeded 
in  producing  good  flint-glass,  and  discs  of  from  12  to  14 
inches.  In  1848,  M.  Bontemps  was  induced  to  accept 
the  invitation  of  Messrs.  Chance,  Brothers  &  Co.,  of 
Birmingham,  England,  to  unite  with  them  in  the  attempt 
to  improve  the  quality  of  glass.  They  have  succeeded 
in  producing  a  disc  in  flint  of  29  inches  in  diameter, 
weighing  200  pounds,  and  of  crown-glass  up  to  20 
inches.  The  former  disc  was  exhibited  at  the  London 
Exposition  of  1851,  and  was  found  to  be  entirely  free 
from  any  striae,  except  a  small  portion  near  one  of  its 
edges.  A  council  medal  was  awarded  to  Messrs.  Chance 
for  this  disc. 

The  following  is  a  list  of  prices  by  Chance,  Brothers 
&  Co.,  of  Birmingham,  for  warranted  first  quality  discs 
of  flint  or  crown-glass : 


inches  diameter,  £2  OOs. 

"            "  27 

"            "  2  15 

"            "  3  15 

"            "  5  00 


6  inches  diameter, 
64-          «  " 

7  "  " 


£7    4s. 
9  10 
12  00 
14  10 
17  00 


384 


HISTORY  OF  ASTKONOMY. 


8£  inches  diameter,    £19  15s. 

9  "  "  22  10 

9£  «  "  25  10 

10  "  •     "  28  10 
10i  "  "  31  10 

11  «  "  35  00 
H  "  "  39  10 


12  inches  diameter,    £44  OOs. 
12$  "  "t  50  00 

13  "  "  57  15 
13$  "  "  65  00 

14  "  "  75  00 
14$  "  "  85  00 

15  "  "  100  00 


M.  Maes,  of  Clichy,  near  Paris,  exhibited  at  the  Lon- 
don, and  also  at  the  New  York  Expositions,  specimens 
of  a  new  kind  of  glass,  the  basis  of  which  is  the  oxyd  of 
zinc,  a  certain  quantity  of  boracic  acid  being  added.  Its 
extreme  limpidity,  and  total  freedom  from  color,  and,  so 
far  as  appears,  from  veins  and  striae,  seem  eminently 
to  fit  it  for  optical  purposes;  but  this  glass  has  not 
stood  as  yet  sufficient  time  to  determine  its  real  value. 
A  prize  medal  was  awarded  to  M.  Maes  at  the  London 
Exposition. 

The  establishment  of  M.  Guinand,  at  Paris,  is  now 
conducted  by  M.  Feil,  grandson  of  P.  L.  Guinand,  and  the 
following  are  the  prices  at  which  he  furnishes  discs  of 
either  crown  or  flint-glass  of  the  first  quality  for  tele- 
scopes : 

4  inches  diameter,      60  francs. 

5  "  "  100      " 

6  "  "  200      " 

7  «  «          250       " 

8  "  "  400       " 


450 


10  inches  diameter,     500  francs. 

11  "  "  550      " 

12  "  "  600   " 
14  "  "    1000   ' 
16  "  u    2000   " 
20  "  "    6000   " 


Mr.  Joseph  Baden,  of  Kohlgrub,  in  Bavaria,  was  for- 
merly a  workman  in  the  establishment  of  Utschneider, 
at  Munich,  but  for  many  years  has  conducted  an  es- 


THE  MANUFACTURE  OP  TELESCOPES.  385 

tablishment  on  his  own  account.  He  makes  large  discs 
both  of  flint  and  crown-glass  of  the  very  best  quality 
fbr  telescopes. 

While  experiments,  made  in  this  country  with  Ameri- 
can glass,  have  generally  proved  failures,  experiments 
with  the  aid  of  foreign  glass  have  been  more  success- 
ful. Three  artists  have  specially  distinguished  them- 
selves in  the  manufacture  of  refracting  telescopes,  viz., 
Mr.  Henry  Fitz,  of  New  York ;  Mr.  Alvan  Clarke,  of 
Boston ;  and  Mr.  Charles  A.  Spencer,  of  Canastota,  New 
York. 

TELESCOPES  BY  HENRY  FITZ,  OF  NEW  YORK. 

Mr.  Fitz's  first  telescope  was  a  Cassegrain  reflector  of 
six  inches  aperture,  and  three  feet  focal  length,  which 
was  constructed  in  1838.  In  1844  he  saw  the  fine 
Munich  telescope  of  the  Philadelphia  High  School 
observatory,  and  determined  to  attempt  the  construction 
of  an  achromatic.  In  this  he  succeeded  by  first  making 
a  lens  of  three  inches  aperture,  and  afterward  one  of 
3f  inches,  being  the  largest  piece  of  flint  glass  he  could 
obtain.  The  quality  of  both  of  these  lenses  was  im- 
paired by  veins,  as  the  concave  lens  was  of  quite 
ordinary  table-ware  glass ;  still,  they  compared  so  favor- 
ably with  good  Munich  telescopes,  that  Mr.  Fitz  im- 
mediately commenced  one  of  six  inches  aperture.  This 
was  also  filled  with  striae,  excepting  in  the  convex  lens, 
which  (like  the  first  two)  was  made  of  French  mirror 
plate.  This  telescope  was  examined  by  the  late  S.  C. 


386  HISTOEY   OF  ASTRONOMY. 

Walker,  and  by  Professor  Kendall,  at  the  Philadelphia 
High  School,  and  elicited  high  approbation.  In  1849, 
Mr.  Fitz  completed  a  telescope  of  6f  inches  aperture  for 
ihe  use  of  the  Chilian  expedition,  and  this  was  the 
first  telescope  composed  of  proper  crown  and  flint  discs, 
all  his  previous  telescopes  having  been  made  of  French 
mirror  plate  convex  lenses,  instead  of  the  superior  op- 
tical crown,  of  which  he  was  hitherto  ignorant.  Since 
1849,  Mr.  Fitz  has  been  continually  increasing  the  size 
of  his  object-glasses,  until  he  has  at  last  attained  to  the 
dimensions  of  the  largest  instruments  furnished  by 
Merz  and  Mahler,  of  Munich.  We  shall  enumerate  the 
principal  telescopes  which  have  been  furnished  by  Mr. 
Fitz,  commencing  with  those  of  the  largest  size. 

No.  1  has  a  clear  aperture  of  12|  inches,  and  a  focal 
length  of  17  feet.  It  has  7  negative  and  6  positive  eye- 
pieces, the  highest  magnifying  power  being  1200.  The 
decimation  circle  is  20  inches  in  diameter,  graduated  to 
20',  and  reads  by  four  verniers  to  20".  The  right  ascen- 
sion circle  is  20  inches  in  diameter,  graduated  to  20', 
and  reads  by  two  verniers  to  two  seconds  of  time.  The 
telescope  is  moved  by  clock-work,  and  is  furnished  with 
a  micrometer.  This  telescope  was  sold  to  the  Michigan 
University  for  $6000.  Dr.  Briinnow,  the  director  of  the 
Michigan  observatory,  pronounces  this  telescope  to  be  a 
good  one,  and  says  that  it  compares  favorably  with  the 
Munich  instruments  of  large  size.  The  six  stars  in  the 
trapezium  of  Orion  are  visible  without  difficulty,  and 
Enceladus  appears  well  at  all  times.  The  discs  of  the 


THE  MANUFACTURE  OF  TELESCOPES.  387 

planets,  and'  even  the  brightest  stars,  are  very  well 
defined. 

No.  2  has  an  aperture  of  9^  inches,  and  a  focal  length 
of  14  feet.  It  has  7  negative  and  6  positive  eye-pieces, 
the  highest  magnifying  power  being  1000.  The  circles 
are  of  the  same  size  as  in  No.  1.  This  telescope  was 
sold  to  West  Point  Academy  for  $5000. 

No.  3  has  an  aperture  of  9  inches,  and  a  focal  length 
of  9£  feet.  The  highest  magnifying  power  is  600.  This 
telescope  was  sold  to  Mr.  Eutherford,  of  New  York,  for 
$2,200.  It  was  made  with  an  unusually  short  focus,  to 
accommodate  the  size  of  Mr.  Eutherford's  dome.  The 
performance  of  this  telescope  is  highly  satisfactory. 

No.  4  has  a  focal  length  of  11  feet,  and  an  aperture 
of  8£  inches.  It  has  twelve  eye-pieces,  the  highest  mag- 
nifying 800  times.  Price,  with  clock-work  and  mi- 
crometer, $2,200;  with  plain  mounting,  $1,600.  Mr. 
Fitz  has  sold  two  telescopes  of  this  size ;  one  to  Mr. 
William  S.  Vanduzee,  of  Buffalo,  N.  Y.,  the  other  to 
the  Friends'  High  School  of  West  Haverford,  Pa. 

No.  5  has  a  focal  length  of  8  feet,  and  an  aperture  of 
6 j  inches.  Highest  magnifying  power  500.  Price,  with 
clock-work  and  micrometer,  $1,300.  Mr.  Fitz  has  sold 
four  telescopes  of  this  size — one  to  Lieutenant  Gilliss,  for 
the  use  of  the  Chili  expedition ;  a  second  to  Mr.  Yan- 
arsdale,  of  Newark,  N.  J. ;  a  third  to  South  Carolina 
College,  Columbia,  S.  C. ;  and  a  fourth  to  Dr.  William 
F.  Hickock,  of  Burlington,  Yt. 

No.  6  has  a  focal  .length  of  7  feet,  and  an  aperture  of 


388  HISTORY    OF  ASTRONOMY. 

5  inches.  Highest  magnifying  power  400  times.  Price, 
with  clock  work  and  micrometer,  $1050  ;  without  clock- 
work and  micrometer,  $825.  Several  telescopes  of  this 
size  have  been  sold. 

No.  7  has  a  focal  length  of  5  feet,  and  an  aperture  of 
4  inches.  Highest  magnifying  power  250  times.  Price 
$225,  without  clock-work  or  micrometer. 

Mr.  Fitz  obtains  his  crown-glass  from  the  manufactory 
of  Bontemps,  of  Birmingham,  England;  his  flint-glass 
he  obtains  from  Paris. 

Several  of  these  instruments  have  been  subjected  to  a 
very  thorough  trial  before  they  were  purchased.  The  in- 
strument for  the  Chilian  expedition  was  procured  under 
the  following  circumstances.  Mr.  Fitz  volunteered  to 
make  an  object-glass  from  Gruinand's  discs,  of  the  same 
dimensions  as  that  of  the  High  School  observatory  in 
Philadelphia,  which  should  be  compared  with  that  in- 
strument, and,  if  pronounced  equal  to  it,  he  should  charge 
for  it  only  the  cost  of  a  similar  lens  at  Munich.  In 
May,  1849,  Professor  Kendall,  of  the  High  School  ob- 
servatory, made  trial  of  the  Fitz  object-glass  upon  the 
moon,  Jupiter,  and  several  double  stars;  and,  after 
careful  comparison  with  his  Fraunhofer,  declared  him- 
self unable  to  pronounce  which  was  the  better  glass. 
Several  other  competent  judges  assisted  at  the  trial,  and 
concurred  with  Professor  Kendall  in  his  opinion.  The 
glass  was  therefore  purchased  by  the  government 
according  to  the  contract.  Lieutenant  Gilliss,  after 
thorough  trial,  pronounced  this  telescope  perfectly 


THE    MANUFACTURE    OF   TELESCOPES.  389 

satisfactory,  and  says  that  it  readily  shows  the  sixth 
star  in  the  trapezium  of  Orion,  and  the  daily  variations 
in  the  colored  portion  of  Mars. 

TELESCOPES  BY  ALYAN  CLAEK,  OF  BOSTON. 

A  little  more  than  ten  years  since,  Mr.  Alvan  Clark, 
of  Boston,  undertook  the  manufacture  of  telescopes.  His 
first  experiments  were  with  reflectors,  but  being  dissatis- 
fied with  these,  he  attempted  the  manufacture  of  object- 
glasses.  In  1846  and  1848,  he  made  two  object-glasses 
of  East  Cambridge  flint-glass.  Between  them  he  made  a 
telescope,  of  5£  inches  aperture,  of  Gruinand  glass  which 
was  sold  to  Mr.  "Welles,  of  Newburyport.  This  telescope 
separated  the  close  pair  in  the  triple  star  Gamma  Andro- 
meda3,  whose  distance  is  two  fifths  of  a  second,  and  showed 
the  sixth  star  in  the  trapezium  of  Orion  at  intervals, 
though  with  difficulty.  After  these,  Mr.  Clark  made  a 
telescope  of  4f  inches  aperture  with  which  he  discovered 
three  new  double  stars;  and  he  has  made  in  all  more 
than  a  dozen  object-glasses  exceeding  four  inches  aper- 
ture. The  following  is  a  list  of  the  largest  which  he  has 
made: 

1.  His  largest  object-glass  is  of  eight  inches  aperture, 
and  now  in  the  hands  of  Kev.  "W.  E.  Dawes,  of  England, 
unsold.  It  was  sent  to  England  in  October,  1855,  and 
under  date  of  December  20th,  Mr.  Dawes  writes  respect- 
ing it  as  follows:  "  Its  efficiency  is  certainly  greater  than 
that  of  any  other  telescope  I  have  tried,  both  in  defining 
the  features  of  a  planet,  and  in  splitting  close  double 


390  HISTORY   OF   ASTRONOMY. 

stars.  I  have  already  seen  Enceladus  pretty  steadily  at 
the  conj  unctions ;  and  on  the  18th  he  was  so  plainl  y 
visible  near  his  eastern  elongation  that  I  detected 
him  before  I  had  quite  brought  the  eye-piece  up  to 
focus." 

2.  A  telescope  of  7f  inches  aperture,  still  on  hand. 

3.  A  telescope  of  7|-  inches  aperture  and  9|  feet  focal 
length,  was  sold  to  Eev.  W.  E.  Dawes  and  sent  to   En- 
gland in  March,  1854.    The  following  are  the  remarks  of 
Mr.  Dawes  respecting  it : 

"  Though  the  crown-glass  has  a  considerable  number 
of  small  bubbles,  the  performance  of  the  telescope  is  not 
sensibly  affected  by  that  circumstance.  In  other  respects 
the  materials  are  good ;  and  the  figure  is  so  excellent,  and 
so  uniform  throughout  the  whole  of  the  area,  that  its 
power  is  quite  equal  to  any  thing  which  can  be  expected 
of  the  aperture ;  and  consequently  both  in  its  illuminat- 
ing and  refracting  powers,  it  is  decidedly  superior  to  my 
old  favorite  of  6£  inches  aperture.  As  a  specimen  of  its 
light,  I  may  mention  the  companion  of  v  Ursa  Majoris  as 
having  been  pretty  steadily  seen  with  it ;  and  also  that  I 
have  never  seen  Saturn  under  tolerable  circumstances 
during  the  present  apparition  without  detecting  Encela- 
dus, even  when  at  or  very  near  his  conjunction  with  the 
planet.  When  exterior  to  or  tangent  to  the  extremity  of 
the  ring,  this  satellite  has  frequently  been  perceived  as 
soon  as  my  eye  was  applied  to  the  telescope.  Last 
spring,  it  was  seen  several  times  in  strong  twilight.  In 


THE   MANUFACTURE   OF  TELESCOPES. 

separating  power,  the  glass  is  competent  to  divide  a  sixth- 
magnitude  star  composed  of  two  equal  stars,  whose  central 
distance  is  0".6." 

Mr.  William  Lassell,  of  Liverpool,  in  a  letter  to  the 
author,  dated  July,  1855,  says  of  this  telescope :  "  The 
optical  efforts  of  Mr.  Clark  have  greatly  astonished  me. 
I  have  had  an  opportunity  of  observing  with  his  tele- 
scope, purchased  by  Mr.  Dawes,  and  I  consider  it,  so  far 
as  I  can  judge,  unsurpassed  if  not  unequaled" 

Mr.  Dawes  paid  $930  for  this  telescope,  and  had  it  fitted 
to  his  Munich  equatorial  stand. 

4.  A  telescope  of  7|  inches  aperture  and  a  .focal  dis- 
tance of  101  inches,  sold  to  Amherst  College.     This  tele- 
scope has  a  pendulum  driving  clock  with  Bond's  spring- 
governor,  and  is  so  arranged  with  a  sector  clamping  upon 
the  polar  axis,  that  its  motion  is  remarkably  equable  and 
firm.    The  circles  are  12  inches  in  diameter;  the  right 
ascension  circle  reading  by  verniers  to  two  seconds  of 
time,  the  declination  circle  to  SO*  of  arc.     The  price  of 
this  telescope  was  $1800. 

5.  A  telescope  of  7j  inches  aperture,  sold  to  Williams 
College  for  $900.     The  equatorial  mounting  was  made  by 
Phelps  and  Gurley. 

6.  A  telescope  of  6£  inches  aperture  was  ordered  by 
Baron  de  Rottenburg,  for  subscribers  in  Kingston,  Canada 
West.     This  telescope  had  a  plain  equatorial  mounting 
and  was  furnished  for  $850. 

The  following  is  a  list  of  the  double  stars  which  Mr. 


392  HISTORY   OF  ASTRONOMY. 

Clark  has  discovered  with,  telescopes  of  his  own  manu- 
facture : 

Right  Ascension.    South  Declination. 

61,  42m.  10s.  140  B8,  47,,  Mag.  6.  j  Discovered  ^  ^  4| 

8  Sextantis,  9k  45m.    4s.  7°  24'    1"     «  4.  Lh  object    lass> 

12h.    Om.  20s.  19°  31'  45"     "  7.  ) 

95  Ceti,          3h.  10m.  42s.  1°  28'  48"     "  6*.  )  Discovered  with  the  H 

6h.    4m.  19s.  4°  38'  11"     "  6£.  Hnch,  sold  to  Mr.  Dawes. 

18h.  17m.  11s.  1°  39'  23"     "  6|.  >  Discovered  with  the  Am- 

19h.  50m.  353.  2°  38'    1"     "  6£.  \  herst  College  telescope. 

Mr.  Clark  is  now  engaged  on  a  model  instrument  de- 
signed to  answer  some  of  the  purposes  of  a  regular  heli- 
ometer.  Its  micrometer  will  embrace  two  degrees,  and 
each  spider  line  be  supplied  with  an  eye-piece  of  high 
power.  Its  efficiency  will  of  course  depend  much  on  the 
accurate  running  of  the  driving  clock,  while  the  observer 
is  passing  his  eye  from  one  object  to  the  other.  By  re- 
moving one  of  the  eye-pieces,  it  becomes  an  ordinary 
micrometer  for  all  small  distances. 

TELESCOPES  BY  CHARLES  A.  SPENCER,  OF  CANASTOTA 
NEW  YORK. 

Mr.  Spencer  has  long  been  celebrated  for  the  ex- 
cellence of  his  microscopes.  In  1851,  a  committee  of 
the  American  Association  for  the  Advancement  of 
Science,  consisting  of  Professor  J.  W.  Bailey,  Dr.  J. 
Torrey,  Professor  J.  Lawrence  Smith,  Dr.  W.  J.  Burnett, 
and  Dr.  Clark,  made  a  report  on  Spencer's  microscopes, 
awarding  the  highest  prize  to  his  lenses,  and  concluded 
with  the  remark,  "the  committee  believe  it  would  be  an 


THE   MANUFACTURE  OF  TELESCOPES.  393 

act  of  injustice  not  to  state  their  sincere  conviction  that 
Spencer's  objectives  are  now  the  best  in  the  world" 

Mr.  Spencer  has  recently  turned  his  attention  to  the 
manufacture  of  refracting  telescopes,  and  his  success  in 
this  department  promises  to  be  as  great  as  in  the  manu- 
facture of  microscopes.  His  principal  telescope  is  one 
recently  completed  for  Hamilton  College,  having  an 
aperture  of  13^  inches  and  a  focal  length  of  nearly  16 
feet.  The  flint  and  crown  discs  for  this  instrument  were 
procured  through  the  agents,  Messrs.  Cook,  Beckel,  &  Co., 
New  York,  from  Joseph  Bader  of  Kohlgrub,  and  have 
been  found  to  be  remarkably  exempt  from  striae.  Among 
the  changes  that  have  been  introduced  in  the  construction 
of  this  instrument,  is  a  method  of  procuring  an  absolute 
optical  collimation  of  the  object-glass,  combined  with  the 
usual  means  of  making  this  axis  coincident  with  the 
axis  of  the  tube.  The  method  used  to  produce  this  re- 
sult enables  the  observer  instantly  to  detect  the  existence 
of  any  error  in  respect  to  collimation ;  and  a  further  ad- 
vantage of  the  construction  is  that  the  object-glass  may 
be  made  to  take  any  angle  of  position  to  the  declination 
axis,  or  to  a  line  joining  the  components  of  a  system  of 
double  stars.  The  focal  length  of  the  object-glass  is 
unusually  short  for  its  aperture ;  and  to  increase  its  mag- 
nifying power,  an  equivalent  of  twice  its  focal  length  is 
obtained  by  the  introduction  of  a  negative  achromatic 
near  the  eye-piece.  The  higher  of  the  six  negative  eye- 
pieces that  belong  to  this  instrument  are  solid,  and  of  a 
construction  radically  different  from  any  heretofore  used. 


394  HISTORY  OF  ASTRONOMY. 

They  are  found  to  be  singularly  free  from  that,  milkiness 
arising  from  diffused  light  and  reflected  images  which 
invariably  exist  in  the  usual  construction.  The  field  of 
view  appears  strikingly  black  and  impressive.  Eamsden's 
form  has  been  wholly  discarded  in  the  positive  eye-pieces 
belonging  to  the  micrometer.  These  have  been  made 
achromatic  and  orthoscopic.  Each  is  composed  of  two 
double  cemented  achromatics  so  calculated  as  to  give  a 
perfectly  flat  field 

In  the  year  1855,  Mr.  Spencer  constructed  an  object- 
glass  of  nine  inches  aperture  and  ten  feet  focal  length,  of 
discs  made  by  Bontemps.  From  the  few  trials  that  have 
been  made  with  it,  its  performance  is  considered  excel- 
lent. Mr.  Spencer  has  also  made  two  object-glasses  of 
5|-  inches  aperture  and  seven  feet  focal  length,  besides  a 
large  number  of  smaller  sizes.  In  their  construction,  he 
has  employed  discs  made  by  Bontemps,  Bader,  Guinand, 
Maes,  and  Daguet. 

Mr.  Spencer  has  recently  received  an  order  for  a  large 
heliometer  for  the  Dudley  observatory,  at  Albany,  at  the 
contract  price  of  $14,500.  The  object-glass  of  this  instru- 
ment is  to  be  of  ten  inches,  clear  aperture. 

Mr.  Spencer  has  recently  visited  the  observatories  and 
workshops  of  England,  France,  and  Germany,  preparatory 
to  the  opening  of  a  large  optical  establishment  at  Albany, 
in  connection  with  Professor  A.  K.  Eaton  and  Mr.  B.  F. 
Baker. 


POSTSCRIPT. 

The  following  notice  was  received  too  late  for  inser- 
tion in  its  proper  place  in  Chapter  IV.,  Section  I. 

HAVERFORD   OBSERVATORY. 

This  observatory  is  situated  about  nine  miles  west 
of  Philadelphia.  The  building  is  of  stone,  and  consists 
of  a  central  part  about  20  feet  square,  and  of  about  the 
same  height,  with  two  wings,  each  15  feet  square,  and  is 
surmounted  by  a  revolving  dome  19  feet  in  diameter. 
The  instruments  are  an  equatorial  telescope ;  a  meridian 
transit  circle  ;  a  prime  vertical  transit ;  a  sidereal  clock  ; 
and  Bond's  magnetic  register.  The  equatorial,  by  Henry 
Fitz,  has  an  aperture  of  8|  inches,  and  a  focal  length  of 
11  feet.  It  is  mounted  in  the  Fraunhofer  style,  on  a 
marble  pedestal  8  feet  high,  which  is  supported  by  a 
stone  pier  6  feet  in  diameter,  passing  through  the  floors 
of  the  building,  and  resting  upon  solid  masonry  8  or  10 
feet  below  the  surface  of  the  ground.  This  telescope 
has  an  excellent  spider-line,  and  also  an  annular  mi- 
crometer, with  five  eye-pieces,  magnifying  from  60  to 
500  times.  It  is  provided  with  a  clock-movement. 


396  HISTOKY   OF  ASTRONOMY. 

whose  attachment  is  such  as  allows  the  tube  to  be 
turned  while  the  clock  is  in  operation. 

In  the  west  wing  is  placed  the  meridian  circle,  which 
was  made  by  "W.  J.  Young,  of  Philadelphia.  It  has  an 
excellent  telescope  of  4  inches  aperture,  and  5  feet  focus, 
with  two  circles  26  inches  in  diameter,  one  of  which 
reads  by  four  verniers  to  two  seconds  of  arc ;  the  other 
is  used  simply  as  a  finder.  The  instrument  is  supported 
by  marble  piers,  five  feet  high,  firmly  based  on  masonry. 

In  the  eastern  wing  is  a  sidereal  clock  by  Harpur, 
of  Philadelphia ;  and  in  the  same  room  is  the  magnetic 
register.  Upon  an  inward  projection  of  the  eastern 
wall  of  the  center  building,  is  mounted  a  prime  vertical 
transit  instrument  20  inches  in  length,  made  by  Dollond. 
This  is  included  in  the  dome  containing  the  equatorial. 
The  cost  of  the  building  was  $2,500,  and  that  of  the 
instruments  contained  in  it  about  $4,500.  This  ob- 
servatory is  in  charge  of  Professor  Joseph  G.  Harlan. 


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